Mishkat al-Masabih 7 Fasting كتاب الصوم 112

وَعَنْ جَابِرِ بْنِ سَمُرَةَ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَأْمُرُ بِصِيَامِ يَوْمِ عَاشُورَاءَ وَيَحُثُّنَا عَلَيْهِ وَيَتَعَاهَدُنَا عِنْدَهُ فَلَمَّا فُرِضَ رَمَضَانُ لَمْ يَأْمُرْنَا وَلَمْ يَنْهَنَا عَنْهُ وَلم يتعاهدنا عِنْده. رَوَاهُ مُسلم

Jabir b. Samura said, “God’s messenger used to command us to observe the day of ‘Ashura’ as a fast, urge us to observe it and pay attention to us when it came; but when Ramadan was made obligatory he neither commanded nor forbade us to observe it, nor did he pay attention to us when it came.” Muslim transmitted it.