Hadith e Thaqalain is a very famous and authentic Hadith in Sunni sources. PLease find here Hadith e Thaqalain in Sahih Muslim, Please also find Hadith e Thaqalain in Trimdhi.
We have presented a separate article on our main page about Ahlalbait, Who are Ahlalbait?
Please find the Hadith e Thaqalain along with Hadith e Ghadir narrated by Zaid bin Arqam (rz) in Nissaie.
Zaid bin Arqam narrated:
When the Holy Prophet returned back from his last pilgrim he stayed on Ghadir e Khumm (A place near mecca). Prophet ordered to make the stage, we put the cloth on that stage then Prophet said “I am about to answer the call (of death) verily, I have left two weighty things among you, one of which is greater than the other, the book of God and my Itra (my Ahlulbayt) so watch out how you succeed me in faring with them, for indeed they will never separate until they return to me by the side of pond. Then he said verily, God is my Mawlaya (master) and I am the wali (master) of all believers.”
Then he took Ali’s hand and declared to whomever I am his wali, this one is also his wali(master) may Allah be friend whoever befriends him and be hostile to whoever is hostile to him. Abu Al Tufayl says, I said to Zaid did you hear it from the Prophet? He replied “There is no one in the caravan who did not see it with his eyes and hear it with his ears”.