The Quran

مِنَ المُؤمِنينَ رِجالٌ صَدَقوا ما عاهَدُوا اللَّهَ عَلَيهِ ۖ فَمِنهُم مَن قَضىٰ نَحبَهُ وَمِنهُم مَن يَنتَظِرُ ۖ وَما بَدَّلوا تَبديلًا

Muhammad Asad

Among the believers are men who have [always] been true to what they have vowed before God;¹ and among them are such as have [already] redeemed their pledge by death, and such as yet await [its fulfilment] without having changed [their resolve] in the least.

Specifically, this verse is said to apply to certain of the Companions who vowed, at the time of the early campaigns, that they would fight until death at the Prophet's side (Zamakhshari); in its wider sense, however, it relates to all efforts involving a supreme sacrifice in God's cause.