It is narrated from the Mother of the Believers, Sayyidah Aishah al-Siddiqah (may Allah be pleased with her), that the Prophet (peace and blessings be upon him) would pray sitting and recite in that state. When thirty or forty verses remained, he (peace and blessings be upon him) would stand up and recite them while standing, then bow and prostrate. Then in the second rak'ah he would do likewise.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3682