Musnad Ahmad 30:3498

Rawh narrated to us, Hammad narrated to us, from Muhammad ibn ‘Amr, from Abu Salamah, from Abu Hurayrah, from the Prophet (peace and blessings of Allah be upon him), who said: "If one of you hears the call (to prayer) while the vessel is in his hand, let him not put it down until he has fulfilled his need from it."