Sahih Ibn Hibban 3661

Translation

✧ The Messenger of Allah ﷺ observed i'tikaf during the middle ten days of Ramadan, seeking Laylat al-Qadr. Then he ordered that a structure be built, but it was dismantled. Then it was made clear to him that it was in the last ten days, so he ordered that it be rebuilt. He came out to us and said, "Laylat al-Qadr was made clear to me, and I came out to make it clear to you, but two men argued and I was made to forget it. So seek it in the ninth, the seventh, and the fifth." I said, "O Abu Sa'id, you know numbers better than us. Which night is the ninth, the seventh, and the fifth?" He said, "When it is the twenty-first night, then skip a night; the one after it is the seventh. Then skip a night, and the one after it is the fifth."

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