Musnad Ahmad 31:114

Hassan narrated to us, Zuhair narrated to us, from Sa’d Abu al-Mujahid al-Ta’i, from ‘Atiyyah ibn Sa’d al-‘Awfi, from Abu Sa’id al-Khudri—I believe he attributed it to the Prophet, may Allah bless him and grant him peace—who said: "Any believer who gives a believer a drink when he is thirsty, Allah will give him to drink on the Day of Resurrection from the sealed nectar (al-rahiq al-makhtum). And any believer who feeds a believer when he is hungry, Allah will feed him from the fruits of Paradise. And any believer who clothes a believer with a garment when he is naked, Allah will clothe him from the green garments of Paradise."