Surah At-Tawbah 9:43

عَفَا ٱللَّهُ عَنكَ لِمَ أَذِنتَ لَهُمْ حَتَّىٰ يَتَبَيَّنَ لَكَ ٱلَّذِينَ صَدَقُوا۟ وَتَعْلَمَ ٱلْكَـٰذِبِينَ

Allāh has pardoned you, [O Muḥammad, but] why did you give them permission [to remain behind]? [You should not have] until it was evident to you who were truthful and you knew [who were] the liars.

Translation: Saheeh International

Tafsir

The Prophet s exercising his personal judgement had given leave to a group to stay behind and so the following was revealed as a reprimand for him but with the pardon first in order to reassure his heart May God pardon you! Why do you give them leave to stay behind; …

Excerpt from Tafsir al-Jalalayn, commentary on 9:43, via Quran.com. The reader has the full commentary and 9 more tafsirs.