In Sahih Muslim, the hadith al-thaqalayn is narrated as follows:
"Yazid b. Hayyan reported, I went along with Husain b. Sabra and 'Umar b. Muslim to Zaid b. Arqam and, as we sat by his side, Husain said to him:
Zaid. you have been able to acquire a great virtue that you saw Allah's Messenger (ﷺ) listened to his talk, fought by his side in (different) battles, offered prayer behind me. Zaid, you have in fact earned a great virtue. Zaid, narrate to us what you heard from Allah's Messenger (ﷺ).
He said: I have grown old and have almost spent my age and I have forgotten some of the things which I remembered in connection with Allah's Messenger (ﷺ), so accept whatever I narrate to you, and which I do not narrate do not compel me to do that.
He then said: One day Allah's Messenger (ﷺ) stood up to deliver sermon at a watering place known as Khumm situated between Mecca and Medina. He praised Allah, extolled Him and delivered the sermon and. exhorted (us) and said: Now to our purpose. O people, I am a human being. I am about to receive a messenger (the angel of death) from my Lord and I, in response to Allah's call, (would bid good-bye to you), but I am leaving among you two weighty things: the one being the Book of Allah in which there is right guidance and light, so hold fast to the Book of Allah and adhere to it. He exhorted (us) (to hold fast) to the Book of Allah and then said: The second are the members of my household I remind you (of your duties) to the members of my family."
Online source - https://sunnah.com/muslim/44/55
for more details on the hadith of Thaqalayn and its study from the hadith books of the Sunni school.