From Sahih Muslim (Hadith 3096):
Abdullah b. 'Umar reported on the authority of his father (Allah be pleased with them):We were along with Allah's Messenger (way peace he upon him) in the morning of 'Arafa (9th of Dhu'l-Hijja). Some of us pronounced Takbir and some of us Tahlil La ilaha ill-Allah). And to those of us who pronounced Takbir, I said: By Allah, how strange it is that you did not care to ask him: What did you see Allah's Messenger (ﷺ) doing (on this occasion)?
Reference: Muslim 3096