Fadl bin Abbas (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Prayer is two rak'ahs at a time, with tashahhud between every two; then fear, humility and lowliness; and raise your hands and turn your face towards the qiblah, and say: 'Ya Rabbi, ya Rabbi' (O my Lord, O my Lord). Whoever does not do so, it is a deficient prayer."
Shu'bah differed from him regarding its chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4577