It is narrated from Sayyiduna al-Fadl bin Abbas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Prayer is two by two (rak'ahs); recite the tashahhud in every two rak'ahs, and show humility, submissiveness and lowliness, and raise both your hands (in supplication); raise them towards your Lord, turning your face towards Him, and say: O my Lord! O my Lord! Whoever does not do so, it (his prayer) is deficient."
Hadith Referenceالمعجم الكبير للطبراني / باب الفاء / 15848