It is narrated from eleventh Shia Imam, Hassan ibn Ali Al-Askari (AS) who said:

But any Faqih (Islamic Jurist) who has self-control and is the guardian/defender of his religion and confronts inordinate desires of his soul, and submits to the command of his Mowla (here, refers to Imam of the time); it is the duty of the people to follow such Faqih. And of course only some of Shia Faqihs have these characteristics, and not all of them [1].

[1] Wasa’elul Shia, Vol. 1, Page 16, Bab 4 from Abwab Sefaat Qadhi, Hadith 33 & Al-Ihtijaj, Vol. 2, Page 510, Hadith 337.

Source: en.shafaqna.com