Surah 4. An-Nisaa', Ayah 17

The expression min qarib, which here implies nearness in time, could also be rendered as "soon", i.e., soon after having committed the evil deed; most of the classical commentators however, hold that in this context it denotes the time before the actual approach of death. This interpretation is borne out by the next verse.

 A person’s repentance will be accepted as long as they repent any time before their death. But one should not procrastinate because they do not know when they will die.