The Messenger of Allah ﷺ came out, the prayer was called, and I prayed the dawn prayer with him. Then the Prophet ﷺ turned and found me praying, so he said, "Hold on, Qays. Two prayers together?"I said, "Messenger of Allah, I had not prayed the two rakahs of fajr."He said, "Then there is no harm."
حدثنا محمد بن عمرو السواق البلخي قال حدثنا عبد العزيز بن محمد عن سعد بن سعيد عن محمد بن إبراهيم
خرج رسول الله ﷺ فأقيمت الصلاة فصليت معه الصبح ثم انصرف النبي ﷺ فوجدني أصلي فقال مهلا يا قيس أصلاتان معا قلت يا رسول الله إني لم أكن ركعت ركعتي الفجر قال فلا إذن
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[Sahih]. Abu Dawud also narrated it in the chapter on tawwu, "Whoever misses it, when should he make it up," hadith 1267, and Ibn Majah, hadith 1154, from the hadith of Saad bin Saeed, with this wording. Ibn Khuzayma graded it sahih, 2/164, 165, hadith 1116, though the chain is disconnected. It has a sahih corroborating narration in Daraqutni and Bayhaqi and others, and Ibn Khuzayma graded it sahih, hadith 1116, as did Ibn Hibban, hadith 624, and Hakim, 1/274, 275, and Dhahabi. The hadith has multiple routes of transmission.