Musnad Ahmad 28:21

Sufyan narrated to us, from Sulayman al-Ahwal, from Mujahid, from Abu 'Iyad, from Abdullah ibn Amr ibn al-As: "When the Prophet, peace and blessings of Allah be upon him, forbade the vessels, they said: 'Not everyone finds a waterskin.' So he granted a concession for the earthenware jar that is not coated with pitch."