It is narrated from the Prophet of Islam (PBUH) who said:

O’ dear Ali (AS), your example among the people is the example of the Surah Al-Ikhlas. Whoever recites this Surah once is like he/she has recited one third of the Quran. Whoever recites it twice is like reciting two thirds of the Quran. And whoever recites it three times is like reciting the whole of the Quran. And dear Ali (AS), you are like this, if anyone calls you by his/her heart, such a person loves you in his/her heart, this person has attained one third of the belief. If anyone calls you with the heart and the tongue, and loves you; has attained two thirds of the belief. If anyone calls you with the heart, and defends you with the tongue, and follows you with all the parts of his/her body, has attained all the belief [1].

[1] Beharul Anwaar, Vol. 39, Page 270.

Source: en.shafaqna.com