Tafseer Ibn Kathir of AL ISRAA' [79]

وَمِنَ اللَّيْلِ فَتَهَجَّدْ بِهِ نَافِلَةً لَّكَ عَسَى أَن يَبْعَثَكَ رَبُّكَ مَقَامًا مَّحْمُودًا

And from [part of] the night, pray with it as additional [worship] for you; it is expected that your Lord will resurrect you to a praised station.