Musnad Abu Ya'la al-Mawsili 140:34

Muhammad ibn Bahr narrated to us, Mu'alla ibn Maymun al-Mujashi'i narrated to us, Yazid al-Raqashi narrated to us, from Anas ibn Malik, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Whoever is kind to a believer or eases for him something of his needs, whether that be small or large, it is a duty upon Allah to have him served by the servants of Paradise."