Sahih Bukhari Volume 6, Book 60, Hadith Number 198.

Narrated By Abdullah bin Ka’b : I heard Ka’b bin Malik talking about the Verse: ‘And to the three (He also forgave) who remained behind.’ (9.118) saying in the last portion of his talk, “(I said), ‘As a part (sign) of my repentance, I would like to give up all my property in the cause of Allah and His Apostle,’ The Prophet said to me, ‘Keep some of your wealth as it is good for you.” (To the three (He also forgave) who remained behind till for them the earth, vast as it is, was straitened…” (9.118)