'A'isha reported that when the Messenger of Allah ﷺ stood up at night to pray, he began his prayer with two short rak'ahs. (Using translation from Muslim 767)
كَانَ رَسُولُ اللهِ ﷺ إِذَا قَامَ مِنَ اللَّيْلِ لِيُصَلِّيَ افْتَتَحَ صَلَاتَهُ بِرَكْعَتَيْنِ خَفِيفَتَيْنِ