عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ رَضِيَ اللَّهُ عَنْهُ أَنَّهُ قَالَ: أَمَرَنَا رَسُولُ اللَّهِ بِيَوْمِ عَاشُورَاءَ أَنْ نَصُومَهُ، وَقَالَ: هُوَ يَوْمٌ كَانَتِ الْيَهُودُ تَصُومُهُ
Narrated by Sayyiduna Jabir bin Abdullah: The Messenger of Allah (peace and blessings be upon him) commanded us to fast on the 10th of Muharram; the Jews used to fast on this day.