Surah Al-Anbya 21:86

وَأَدْخَلْنَـٰهُمْ فِى رَحْمَتِنَآ ۖ إِنَّهُم مِّنَ ٱلصَّـٰلِحِينَ

And We admitted them into Our mercy. Indeed, they were of the righteous.

Translation: Saheeh International

Tafsir

And We admitted them into Our mercy through granting them prophethood. Indeed they were among the worthy of it. Dhū’l-Kifl was so called because he undertook takaffala to fast every day and stay up every night in prayer and to pass judgement between people without succumbing to anger and fulfilled this undertaking. …

Excerpt from Tafsir al-Jalalayn, commentary on 21:86, via Quran.com. The reader has the full commentary and 9 more tafsirs.