I saw the Messenger of Allah ﷺ throw the pebbles on the Day of Sacrifice in the forenoon, and that was the only time he did so then. After that day, he would throw them after the sun had passed its zenith.
حدثنا يحيى عن ابن جريج أخبرني أبو الزبير قال سمعت
رأيت رسول الله ﷺ يرمي يوم النحر ضحى وحده وأما بعد ذلك فبعد زوال الشمس
Its chain of transmission is sahih. It is found in Tirmidhi, 3/138, no. 894, in the book of Hajj, in the chapter on what has been said about throwing the pebbles on the day of sacrifice in the morning, and he said, hasan sahih. It is also found in Abu Dawud, 1971, in the book of Hajj, in the chapter on throwing the pebbles.