Imam as-Sadiq (‘a) said: "He who seeks the company of those who insult the lovers of Allah has surely disobeyed Him, the Sublime."
Usul al-Kafi, vol. 2, p. 379
Imam as-Sadiq (‘a) said: "When you are informed of a fellow companion committing an evil action, then go to him and tell him: 'O so and so! Either refrain from committing this sin or keep away from us'; then, avoid him unless he does so."
Wasa'il-ush-Shi'ah, vol. 16, p. 146
Imam as-Sadiq (‘a) has narrated from his father Imam Muhammad Baqir (‘a) who said his father ‘Ali ibn Husayn (‘a) stated: "O' my son! Beware of five (groups) and do not seek companionship with them, do not speak with them, and do not make friends with them on (the) way."
Then, Imam al-Baqir (‘a) asked his father who they were and might he introduce them to him. He responded:
"Beware of and do not associate with the one who tells lies. He is as a mirage which makes near for you what is far, and makes far to you what is near."
"Beware of and do not associate with an immoral person, because he will sell you at the price of a morsel or less than that."
"Beware of and do not associate with a miser because he will deprive you of his wealth when you are seriously in need of it."
"Beware of and do not associate with a fool, because he wants to be of avail to you but he harms you."
"Beware of and do not associate with the one who disregards his kinfolks, because I found him (such a person) cursed in the Book Allah, Almighty and Glorious, in three occurrences."
They are: Sura Al-Baqarah, No.2, verse 27; Sura Ar-Ra'd, No.13, verse 25; and Sura Muhammad, No.47, verse 22.
Al-Kafi, vol. 2, p. 641
Imam Amir-ul-Mu'mineen ‘Ali (‘a) said: "O' Kumayl! Say what is just in any condition. Be friends with the righteous and avoid the evil doers, stay away from the hypocrites and do not accompany the treacherous."
Mustadrak-ul-Wasa'il, vol. 12, p. 197