Sahih al-Bukhari 3114
One-fifth of Booty to the Cause of Allah (Khumus)
The Statement of Allah Taa'la: "Verily one-fifth of it is assigned to Allah and to the Messenger ﷺ ..."
Narrated Jabir bin 'Abdullah (ra): A boy was born to one of our men, the Ansar, and he wanted to name him Muhammad. Then Ansari man said, "I took the boy to the Prophet (ﷺ). The Prophet (ﷺ) said, "Name your child by my name, but do not name (them) by my Kunya, for I have been made Qasim (i.e., a distributor) to distribute (the booty etc.) amongst you." The narrator, Husain said that the Prophet (ﷺ) said, "I have been sent as a Qasim (i.e., distributor) to distribute (things) amongst you." [The Sub narrator Salim said that he heard Jabir saying that the man wanted to name the boy Al-Qasim, but the Prophet (ﷺ) said, "Call (your sons) by my name, but do not name (them) by my Kunya."]