It is narrated from Hazrat Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) used to perform Witr with nine rak'ahs. Then, when his age increased and his blessed body became heavy, the Prophet (peace and blessings be upon him) started performing Witr with seven rak'ahs. Then the Prophet (peace and blessings be upon him) would offer two rak'ahs while sitting. The previous hadith is also narrated through this second chain.