From Sahih Bukhari (Hadith 246):
Narrated Ibn 'Umar:The Prophet (ﷺ) said, "I dreamt that I was cleaning my teeth with a Siwak and two persons came to me. One of them was older than the other and I gave the Siwak to the younger. I was told that I should give it to the older and so I did
Reference: Bukhari 246