Surah Al-Hijr, ayah 99

15:99

وَٱعۡبُدۡ رَبَّكَ حَتَّىٰ يَأۡتِيَكَ ٱلۡيَقِينُ ٩٩

Wa'bud rabbaka hattā ya'tiyakal-yaqīn

And worship your Lord until there comes to you the certainty [i.e., death].