It is narrated from Hazrat Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) used to tire his body greatly in worship, but when he began to grow older and his blessed body became filled with flesh, the Prophet (peace and blessings be upon him) would often perform prayers while sitting.
Hadith Referenceمسند احمد / مسند النساء / 25360
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف لتدليس ابن جريج ولابهام أهل عائشة