Musnad Ahmad 33:760

Qutaybah ibn Sa'id 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 indeed, among the acts of kindness is that you meet your brother with a cheerful face, and that you pour from your bucket into your brother's vessel."