Amrah narrates from Sayyidah Aishah (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) would recite while sitting, and when he (peace and blessings be upon him) intended to bow, he would stand for as long as it takes a person to recite forty verses.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4591