Musnad Ahmad 21189

Translation

✧ I said to my father: "Indeed, your brother is taking them from the Mus'haf." It was said to Sufyan ibn Mas'ud, "Is that true?" He did not deny it. He said, "I asked the Messenger of Allah ﷺ, and he said, 'It was said to me, so I said it.' " Sufyan said, "He used to seek refuge for both of them, and they are not in the Mus'haf of Ibn Mas'ud. He would make them a means of seeking protection for al-Hasan and al-Husayn, but he did not recite them in any part of his prayer. So he thought they were two surahs for seeking refuge and persisted in his belief. Those who came after him confirmed that they are from the Qur'an, so they preserved them and entrusted them to him."

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