Musnad Ahmad 175:25

'Amir ibn Salih narrated to us, he said: Yunus ibn Yazid narrated to me, from Ibn Shihab, from 'Abd al-Rahman ibn Ka'b ibn Malik al-Ansari, from his father, that he said to the Messenger of Allah (may Allah bless him and grant him peace) when Allah (Blessed and Exalted is He) accepted his repentance: "O Messenger of Allah, shall I divest myself of my wealth as charity to Allah and His Messenger?" The Messenger of Allah (may Allah bless him and grant him peace) said to him: "Keep some of your wealth, for it is better for you."