Sahih al-Bukhari 4841
Narrated `Uqba bin Sahban:
`Abdullah bin Mughaffal Al-Muzani who was one of those who witnessed (the event of) the tree, said, 
"The Prophet (ﷺ) forbade the throwing of small stones (with two fingers)."
حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا شَبَابَةُ، حَدَّثَنَا شُعْبَةُ، عَنْ قَتَادَةَ، قَالَ سَمِعْتُ عُقْبَةَ بْنَ صُهْبَانَ، عَنْ عَبْدِ اللَّهِ بْنِ مُغَفَّلٍ الْمُزَنِيِّ، إِنِّي مِمَّنْ شَهِدَ الشَّجَرَةَ، نَهَى النَّبِيُّ صلى الله عليه وسلم عَنِ الْخَذْفِ‏.‏