(a) Khalid bin Sumayr narrates that Abdullah bin Rabah al-Ansari came to us, and the Ansar used to regard him as a jurist (faqih). He said: Abu Qatadah (may Allah be pleased with him), the horseman of the Messenger of Allah (peace and blessings be upon him), narrated the hadith to us.
Then he mentioned the complete hadith about the prayer being missed because of sleep, and said: When the sun had risen and become quite high, we woke up and began to hurry to the prayer, but the Prophet (peace and blessings be upon him) said: "Wait, so that the sun rises fully." Then, when the sun had become quite high, he said: "Whoever prays the two rak'ahs (sunnah) of Fajr, let him pray them." So all the people stood up and offered two rak'ahs. Then the Messenger of Allah (peace and blessings be upon him) ordered the call to be given, and the adhan for the prayer was called. Then the Messenger of Allah (peace and blessings be upon him) stepped forward and led us in prayer. When he had finished the prayer with the salam, he said: "All praise belongs to Allah Almighty (thanks be to Allah) that no worldly occupation made us heedless of our prayer; our souls were in the hand of Allah Almighty, and He released them when He willed." And he said: "Whoever reaches the Fajr prayer on time tomorrow, let him pray another prayer like it along with it."
(b) Imam Muhammad bin Isma'il al-Bukhari (may Allah have mercy on him) says that he is not corroborated in his statement: "Whoever forgets to pray a prayer, let him pray it whenever he remembers it, and offer it at its time the next day."
(c) Imam al-Bayhaqi (may Allah have mercy on him) says: What indicates the weakness of this wording, and that what is authentic is what has passed, is found in the hadith of Sulayman bin al-Mughirah: that Imran bin Husayn (may Allah be pleased with him) was one of the travellers of that same caravan, as Abdullah bin Rabah also narrated from him, and he stated explicitly in his narration of this hadith that nothing besides the make-up prayer is obligatory.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3173