Sahih Ibn Hibban 3633

Translation

✧ I came to Ibn Abbas while he was reclining on his cloak at Zamzam, so I sat with him, and what an excellent companion he was. I asked him about Ashura. He sat up straight and said, "About which aspect of it are you asking?" I said, "About its fasting: which day do we fast?" He said, "When you see the crescent of Muharram, count, then begin the ninth day fasting." I said, "Is that how Muhammad ﷺ used to fast?" He said, "Yes."

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