Musnad Ahmad 31:928

Waki’ narrated to us, Ibn Abi Layla narrated to us, from ‘Atiyyah al-‘Awfi, from Abu Sa’id al-Khudri, who said: The Prophet (peace and blessings of Allah be upon him) said: "Charity is not lawful for a wealthy person except for three: [one who is] in the way of Allah, or a wayfarer, or a man who had a neighbor and he gave him charity, so he gifted it to him."