عَفَا اللَّهُ عَنكَ لِمَ أَذِنتَ لَهُمْ حَتَّىٰ يَتَبَيَّنَ لَكَ الَّذِينَ صَدَقُوا وَتَعْلَمَ الْكَاذِبِينَ (43)
(9:43) O Prophet, may Allah forgive you: why did you give them leave to stay behind? (You yourself should not have given them leave), so that it would have become clear to you which of them spoke the truth, and you would have also known which of them were liars. *45
*45) Allah did not approve of the exemption which the Holy Prophet had granted to the hypocrites who had put forward lame excuses. Though he knew it well that they were inventing false excuses, he gave them leave to stay behind because of his inherent kindness. But Allah warned him that such a leniency was not well placed as he gave them an opportunity of hiding their hypocrisy. Had they remained behind without getting an exemption, the false profession of their faith would have been exposed.