Sahih Bukhari Volume 6, Book 60, Hadith Number 365.

Narrated By ‘Uqba bin Sahban : ‘Abdullah bin Mughaffal Al-Muzani who was one of those who witnessed (the event of) the tree, said, “The Prophet forbade the throwing of small stones (with two fingers).” ‘Abdullah bin Al-Mughaffal Al-Muzani also said, “The Prophet also forbade urinating at the place where one takes a bath.”