The Messenger of Allah ﷺ as saying: When one of you gets up at night, he should begin the prayer with two short rak'ahs.  

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا قَامَ أَحَدُكُمْ مِنَ اللَّيْلِ فَلْيُصَلِّ رَكْعَتَيْنِ خَفِيفَتَيْنِ  

He should then prolong it afterwards as much as he likes. Abu Dawud said: This tradition has been transmitted by Hammad b. Salamah, Zuhair b. Mu'awiyah and a group of narrators from Hisham. They transmitted it as a statement of Abu Hurairah himself (mauquf). This tradition has also been transmitted by Ibn 'Awn from Muhammad (b. Sirin). This version has the wordings: These two rak'ahs were short.  

إِذَا بِمَعْنَاهُ زَادَ ثُمَّ لْيُطَوِّلْ بَعْدُ مَا شَاءَ  

The Prophet ﷺ was asked: which is the best action? He replied: To stand in prayer for a long time.  

أَنَّ رَسُولَ اللَّهِ ﷺ سُئِلَ أَىُّ الأَعْمَالِ أَفْضَلُ قَالَ طُولُ الْقِيَامِ