It is narrated from Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) led them in five rak'ahs. When he gave the salam, he (peace and blessings be upon him) was told of this, so he (peace and blessings be upon him) faced the qiblah and performed two prostrations while sitting.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9808