We used to fast on Ashura and pay the fitr charity. When Ramadan was revealed and zakat was prescribed, we were neither commanded to do it nor forbidden from it, but we continued to practice it.
كنا نصوم عاشوراء، ونؤدي الفطر، فلما نزل رمضان، ونزلت الزكاة لم نؤمر به ولم ننه عنه، وكنا نفعله.
Nasai (2506) narrated it from Ismail bin Masud, who said, Yazid bin Zuray told us, who said, Shubah reported to us, from Hakam bin Utayba, from Qasim bin Mukhaymara, from Amr bin Shurahbil, from Qays bin Saad, and he related it.Tahawi also narrated it in Mushkil (2258) through the hadith of Rawh bin Ubada, who said, Shubah told us, and he related it. Its chain of transmission is sahih.