Abdullah bin Shaqiq (may Allah have mercy on him) said: I asked Aishah (may Allah be pleased with her) about the prayer of the Prophet (peace and blessings be upon him), and she said: He (peace and blessings be upon him) would often pray standing or sitting. When he (peace and blessings be upon him) began the prayer standing, he would also bow standing, and when he began the prayer sitting, he would also bow sitting.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4583