Musnad Ahmad 33:592

Ishaq ibn Isa narrated to us, al-Munkadir ibn Muhammad ibn al-Munkadir narrated to us, from his father, from Jabir ibn Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Every act of kindness is a charity. And among the acts of kindness is that you meet your brother with a cheerful face, and that you pour from your bucket into his vessel."