It is narrated by Abi Al-Jarood that Imam Ali (as) has said: 

Prophet Ibrahim was passing through the area of Baniqiya, an area that was exposed to many earthquakes, and decided to stay the night there. That night, no earthquake hit the place... .

In the morning, the people kept wondering “How is it that no earthquake hit us last night?” Others said, “An Old man with a young boy lodged in our quarters last night.” So the people of those quarters came to Ibrahim and said: “You! We are struck by earthquakes every night, and it was only last night that no earthquake struck us. Would you please stay for tonight as well?” No earthquake struck that night as well so they went to Ibrahim, saying, “Live with us and we will pay you whatever you ask for!” Ibrahim refused, saying, “No, but if you sell Al-Dhahr* Al-Dhahr to me,  there will be no more earthquakes.” At that, they immediately offered it to him for free, but he refused to take it without paying for it. “You set the price as you see fit,” they said. He paid them four ewes and four donkeys, and that is where the name Baniqiya comes from as part of the word (-iqia) means a ewe. The servant boy then turned to Prophet Ibrahim and said: “O beloved friend of Allah! What are you going to do with this area when no plants can grow on its lands and no cattle can graze in it.” The prophet replied: “Hush! Indeed Allah the Almighty will resurrect 70 thousand people from this Dhahr, all who will enter paradise without reckoning. Each and every one of them will have the privilege of interceding for others to enter with them, no matter their amount.”

Abu Saeed Al-Khudri narrated that the Messenger of Allah had said:

“Al-Kufa is the skull of the Arabs, the spear of Allah, and the treasure of Faith.”  
The holy city of Najaf is the home of peace, it is the gathering place where the souls of the believers meet after death, it is a spot from the gardens of Eden. Its honor is undeniable. Its privileges—both the everlasting and the transient—are rationally apparent and clear to the people of wisdom and insight. It is for this very reason that Imam Ali (as) chose this spot to be buried in.   

In a narration by al-Mufadhal bin Omar, Imam al-Sadiq (as) says about the land of Al-Ghari:

“It is part of the mountain upon which Allah (swt) directly spoke to Mose, upon which He glorified Jesus majestically, selected Ibrahim as His intimate servant, declared Muhammad as His beloved servant, and designated it to be a resting place for all the prophets.” 

In another narration by Abu Ussama, Imam al-Sadiq (as) says:

“Kufa is an orchard from the orchards of Heaven, embracing the bodies of Noah and Ibrahim, the bodies of three hundred prophets, seventy messengers, and six hundred custodians; and it is home to the tomb of the Master of the Custodians and the Commander of the Faithful, Imam Ali.” 

Hassan bin Mahran narrates that Imam al-Sadiq says:

“I heard Imam Ali once say, “Mecca is the House of Allah and Medina is the house of the Prophet, [but] Kufa is my house any tyrant that brings evil to it will surely be destroyed by Allah.”  

Abu Bakr al-Hadhrami said that he once asked Imam al-Baqir (as), “Which spot is considered the most honorable after the House of Allah and the house of His Messenger?” Imam Baqir replied:

“O Abu Bakr! It is surely Al-Kufa, the pure and sacred land containing the tombs of the prophets, the messengers, and the sincere trustees. It is home to the Sahla Mosque—the mosque that all the prophets of Allah had prayed in. It is from Kufa, that Allah’s justice will appear [Imam Mahdi] along with those who will follow him later on. It is the dwelling of the prophets, the custodians, and the righteous.”

The Messenger of Allah (sawa) said: 
“Ali is the one to whom patience and thankfulness were attributed.”

Al-Kulaini, in his book Al-Qawi, narrates that Younis Bin Wahab Al-Qassri had said: 
Upon arriving in Medina, I visited Imam Al-Sadiq and said to him, “May I offer myself as your ransom! I have come to visit you without visiting  the tomb of Imam Ali [your grandfather].” At that he said, “What a terrible thing to do! If you weren’t of our Shia, I would not look at you ever again. How could you not visit he whom  is visited by Allah, His angels, His prophets, and the believers?” I replied, “May I be offered as your ransom! I did not know!” Imam said: “You should know that Imam Ali (as) is the best of the Imams in the eyes of Allah. He is rewarded as much as they are for their deeds, and Allah rewards them in proportion to their deeds.” 

The Sheikh in his book Al-Qawi, narrates on behalf of Al-Hussain bin Ismaeel al-Sumairi that Imam al-Sadiq (as) said:

“Whosoever visits Imam Ali (as) on foot, will be rewarded for every step they take a reward equal to that of one Hajj and Umrah, and with each step they take as they return home, they will be rewarded double that.” 

Abdullah bin Talha al-Nahdi narrates that he once entered upon Imam al-Sadiq who asked him:

“O Abdullah bin Talha! Do you visit the tomb of my father, Imam Hussain?” The man replied: “Yes, of course we do!” “Do you visit him every Friday?” “No. “Then every month?” “No.” Imam said: “You stay away from him for far too long! His visit equals one Hajj and one Umrah , while visiting the tomb of my father, Ali (as), equals two Hajjs and two Umrahs.” 

The Messenger of Allah (sawa) said: 
“Ali is a trustee—he carries out, on behalf of me, the duties of my religion.”

Jafar bin Muhammad al-Sadiq once told Ibn Marid:

“O Ibn Marid! Whosoever visits the tomb of my grandfather, Ali, while being fully aware of his virtues, will be rewarded by Allah with one accepted Hajj and one blessed Umrah. O Ibn Marid! I swear by Allah that no foot that becomes dusty on its way to the tomb of Imam Ali (as)—whether it came riding or walking—will ever be fed by Allah to the hellfire. O Ibn Marid! Write this down in liquid gold [for it is precious].”  

Abu al-Sa’ai, the preacher of the people of Hijaz, narrated that he entered upon Imam Jafar (as) and said:

“O son of the Messenger of Allah, what reward is there for the one who visits his [Imam Ali] tomb and makes prosperous his lands?” Imam Jafar (as) replied: “O Abu Aamir, my father has narrated from his father, who narrated from his grandfather, Hussain bin Ali, that the prophet (sawa) told Ali, ‘You will surely be killed and buried in the lands of Iraq.” At that, Ali had asked him: “O Messenger of Allah! What reward is there for those who visit our tombs and devote themselves to visiting us?” The prophet replied, “O Abul-Hasan! Allah has made your tombs and the tombs of your sons as spots and courtyards from the Heavens. Moreover, Allah (swt) has made the hearts of the noblest and best of His servants ache in longing for you. It is they who endure pain and humiliation for your sake, erect your tomb, and visit you regularly for the sake of attaining nearness to Allah (swt) and out of love for His Messenger. O Ali! It is they who are worthy of my intercession, it is they who are allowed to drink from my Spring, and it is they who will visit me later in the Heavens.  O Ali! Anybody who erects your tombs and visits them regularly will attain the reward of one who helped Sulayman bin Dawood in building the House of Jerusalem. They will attain the reward of seventy additional pilgrimages to Mecca, after the obligatory pilgrimage (Hajj). Those who visit your tombs return as pure and sinless as the day of their birth, so rejoice and give glad tidings to your followers and to your lovers of blessings that have never been seen, heard, or even imagined by anyone before. The immoral people of my nation will find fault with those who visit your tombs. They will disgrace them for it the way a prostitute is disgraced for her crime. It is they who are the evil-doers of my nation; surely they will not gain my intercession nor will they drink from my Spring.”

In a narration that al-Mufadhal bin Omar al-Ja’afi once entered upon Imam al-Sadiq and said:

“I long for the lands of al-Ghari [Najaf].” The Imam asked him: “What about it do you long for?” Al-Mufadhal replied: “I wish to visit the Commander of the Faithful, Imam Ali (as).” At that, Imam said: “Do you know the merits of visiting him?” “O son of the Messenger of Allah, I do not. Would you inform me of them?” Imam replied: “When you visit the Commander of the Faithful, you should know that you are visiting the bones of Adam, the body of Noah, and  the body of Ali (as). After visiting the side of Najaf, then you should perform the rituals of visiting the bodies of Adam, Noah, and Ali as in doing so you are visiting the first forefathers, the Seal of the Prophets, Muhammad, and the Master of the Custodians, Ali. Truly, Allah opens the doors of Heaven as soon as they call upon Him. So do not be of the negligent and do not be slow in embracing the blessings of this visit. The back part of Kufa is the first spot upon which Allah (swt) was worshipped when He ordered the angels to prostrate themselves to Adam. To its side, there is a tomb where any distressed person who comes and offers four units (Ra’kat) of prayer there will not be disappointed by Allah (swt) and will return happy. We have a saying that states: “At the back of Kufa lies a tomb where any sick person who visits it will be healed.”

The Messenger of Allah (sawa) said: 
“Ali is from me..and I am from Ali.”

When Imam al-Sadiq was asked about the divine blessings one might get from being near to the tomb of Imam Ali and Imam Hussain (peace be upon them both), he said, “Staying the night as a neighbor to the tomb of Imam Ali (as)is better than seven hundred years of worship, and staying the night as a neighbor to the tomb of Imam Hussain (as) is better than seventy years of worship.” On another occasion, however, Imam Sadiq (as) said, “Staying the night at the tomb of Imam Ali (as) is equal to seven hundred years [of worship].”  He (as) was also once asked about the rewards of offering prayer at the tomb of Imam Ali (as): “Performing one prayer at the tomb of the Commander of the Faithful is equal to two hundred thousand prayers elsewhere.”

 Source: imamali-a.com