Musnad Ahmad 582:1

'Abd al-Razzaq narrated to us, Ma'mar informed us, from Ibn Abi Dhi'b, from 'Abdullah ibn al-Sa'ib, from his father, from his grandfather, that he heard the Prophet, may Allah bless him and grant him peace, say: The Messenger of Allah, may Allah bless him and grant him peace, said: "Let not one of you take the property of his companion, neither in earnest nor in jest. And if one of you finds the staff of his companion, let him return it to him."