I am one of those who witnessed the tree. The Prophet ﷺ forbade flicking pebbles.
إني ممن شهد الشجرة، نهى النبي ﷺ عن الخذف.
Bukhari related it in the tafsir (4841) and Muslim in hunting and slaughtered animals (1954:55), both via Shuba, from Qatada, who said, I heard Uqba bin Sahban, from Abdullah bin Mughafal Muzani, and he mentioned it. The wording given is Bukhari's, and Muslim's wording is similar.