Sahih Ibn Khuzaymah 2092 — the Messenger of Allah

It is narrated from Sayyiduna Salamah bin Akwa’ (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said to a man from the tribe of Aslam: “Announce among your people or among the people on the day of ‘Ashura that whoever has eaten should fast for the rest of the day, and whoever has not eaten should observe the fast.”