Musnad Ahmad 5:181

Waki’ narrated to us, Sufyan narrated to us, from Abu Ishaq, from al-Harith, from Ali, who said: Three men came to the Prophet, may Allah bless him and grant him peace. One of them said: "O Messenger of Allah, I had one hundred dinars, and I gave ten dinars of them in charity." The other said: "O Messenger of Allah, I had ten dinars, and I gave one dinar of them in charity." And the other said: "O Messenger of Allah, I had one dinar, and I gave a tenth of it in charity." He said: The Messenger of Allah, may Allah bless him and grant him peace, said: "All of you are equal in reward; all of you gave a tenth of your wealth in charity."