﴿ عَفَا ٱللَّهُ عَنكَ لِمَ أَذِنتَ لَهُمْ حَتَّىٰ يَتَبَيَّنَ لَكَ ٱلَّذِينَ صَدَقُوا۟ وَتَعْلَمَ ٱلْكَٰذِبِينَ ﴾

“May God pardon thee [O Prophet]! Why didst thou grant them permission [to stay at home] ere it had become obvious to thee as to who was speaking the truth, and [ere] thou camest to know. [who were] the liars?”

Please check ayah 9:45 for complete tafsir.