Musnad Ahmad 31:439

'Abd al-Samad and Hasan ibn Musa narrated to us, they said: 'Abd al-'Aziz ibn Muslim narrated to us, Suhayl narrated to us, from his father, from Abu Sa'id al-Khudri, that the Messenger of Allah, peace and blessings of Allah be upon him, said: "Silver for silver, and gold for gold, like for like."