question #3 Sahih al-Bukhari 6690, Book 83, Hadith 67 : How does the concept of expiation relate to repentance and forgiveness in Islamic teachings?

In the last part of his narration about the three who remained behind (from the battle of Tabuk). (I
said) “As a proof of my true repentance (for not joining the Holy battle of Tabuk), I shall give up all
my property for the sake of Allah and His Apostle (as an expiation for that sin).” The Prophet (ﷺ) said (to
me), “Keep some of your wealth, for that is better for you.”