Hadith 1243
Lady Aisha (may Allah be pleased with her) narrates that the Noble Prophet (peace be upon him) used to pray while sitting. And when about thirty or forty verses of the surah remained, he (peace be upon him) would stand up and recite those verses, then bow (ruku‘).
Hadith 1244
Umm al-Mu’minin Aisha (may Allah be pleased with her) narrates that the Messenger of Allah (peace and blessings be upon him) would recite (in voluntary prayer) while sitting, and when he intended to bow (for ruku’), he would stand for as long as it takes a person to recite forty verses, (then he would perform ruku’).