Ziyad bin Ilaqah (may Allah have mercy on him) narrates: Mughirah bin Shu'bah (may Allah be pleased with him) led the prayer and stood up after the first two rak'ahs, so the people alerted him by saying Subhan Allah, but he carried on with his prayer. When he finished, he made the two prostrations of forgetfulness (sajdah al-sahw) and said: "The Messenger of Allah (peace and blessings be upon him) also did it this way."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 18143