سنن أبي داود

Narrated Muttalib:

The Prophet (ﷺ) said: Prayer is to be offered in two rak'ahs; and you should recite the tashahhud at the end of two rak'ahs, and express your distress and humility and raise your hands and say praying: O Allah, O Allah. He who does not do so does not offer a perfect prayer.

Abu Dawud was asked about offering prayer at night in two rak'ahs. He said: They may be two if you like and four if you like.