Musnad Ahmad 1105:1

Yazid ibn Harun narrated to us, Sufyan al-Thawri informed us, from Salamah ibn Kuhayl, from al-Qasim ibn Mukhaymirah, from Abu Ammar, who said: I asked Qays ibn Sa’d about Sadaqat al-Fitr, and he said: "The Messenger of Allah, peace and blessings of Allah be upon him, commanded us [to give it] before Zakat was revealed. Then Zakat was revealed, and we were neither forbidden from it, nor commanded to do it, and we perform it." And I asked him about the fasting of Ashura, and he said: "The Messenger of Allah, peace and blessings of Allah be upon him, commanded us [to fast it] before Ramadan was revealed. Then Ramadan was revealed, and we were neither commanded to do it, nor forbidden from it, and we perform it."