We used to fast on Ashura and pay the zakat of Fitr. 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.
أخبرنا إسمعيل بن مسعود قال حدثنا يزيد بن زريع قال أنبأنا شعبة عن الحكم بن عتيبة عن القاسم بن مخيمرة عن عمرو بن شرحبيل
كنا نصوم عاشوراء ونؤدي زكاة الفطر فلما نزل رمضان ونزلت الزكاة لم نؤمر به ولم ننه عنه وكنا نفعله
[Sahih] Tabarani narrated it in Kabir 18/349, no. 888, from the hadith of Hakam with this wording, and it is also in Kubra, no. 2285. The following hadith serves as a corroborating witness for it. Amr bin Shurahbil is Abu Maysara.