Musnad Ahmad 1053:1

Isma'il narrated to us, Muhammad ibn Ishaq narrated to us, from Yazid ibn Abi Habib, who said: Marthad ibn Abdullah would not come to the mosque except that he had something with him to give in charity. He said: So he came one day to the mosque and he had onions with him. I said to him, "O Abu al-Khayr, what do you intend with this? It will make your garment smell." He said, "O son of my brother, by Allah, there was nothing in my house to give in charity other than it. For a man from the companions of the Prophet, may Allah bless him and grant him peace, narrated to me from the Prophet, may Allah bless him and grant him peace, that he said: 'The shade of the believer on the Day of Resurrection is his charity.'"