The grandfather of Sa'd (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) saw me while I was praying the two rak'ahs of Fajr after the Subh prayer. He (peace and blessings be upon him) said: "O Qays, what are these two rak'ahs?" I said: "O Messenger of Allah, these are the two rak'ahs of Fajr that I had not been able to pray." So the Prophet (peace and blessings be upon him) remained silent.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4391