Imam Ali(as) while prophasising the martryodm of Imam Hasan(as) and Imam Husain(as) said:

سيصيب الذين ظلموا رجزا في الدنيا بسيوف من يسلط الله تعالى عليهم للانتقام بما كانوا يفسقون كما أصاب بني إسرائيل الرجز. قيل و من هو قال غلام من ثقيف، يقال له المختار بن أبي عبيد

“Those people who have done oppression, he will get the return in the world iteself. And that will be such that Allah will overpower them with the one who take our revenge. And their end will be the same as that of Bani Israeel.

People asked: “Who will he be? [the one who will avenge the oppression on the AhlulBait (as)]

Imam Ali (as) said: “A Person from the tribe of Saqeef named Mukhtar bin Abi Obuyda”.

[Source: Tafseer-e-Imam Askari (as) Pg.547 / Bihar Al Anwar Vol.45 Pg.340]

Imam Baqir(as) says:

أبي جعفر الباقر عليه السلام أنه قال لا تسبوا المختار فإنه قتل قتلتنا و طلب بثارنا و زوج أراملنا و قسم فينا المال على العسرة

"Don’t say bad about Mukhtar as he has killed those who killed Us, took the reveneg of Our blood, arranged marriages of Our widows and distributed wealth to the needy people among Us."

[Source: Rijal-e-Kashi Pg.125 / Bihar Al Anwar Vol.45 Pg.343]

أن علي بن الحسين (ع) لما أتي برأس عبيد الله بن زياد و رأس عمر بن سعد، قال فخر ساجدا و قال الحمد لله الذي أدرك لي ثاري من أعدائي، و جزى الله المختار خيرا

Amr bin Ali has narrated that when the heads of Ibne Ziyad and Amre Aas were brought in front of Imam Zainul Abedeen(as) , Imam (as) went in prostration to thank Allah(swt) and said the following words: All thanks if for Allah(swt) who took the revenge from my enemies. May Allah(swt) give good rewards to Mukhtar.

[Source: Rijal-e-Kashi Pg.127 / Bihar Al Anwar Vol.45 Pg.344]