On one occasion in battle, Usama ibn Zayd killed a man who had uttered the testimony of faith. The Messenger ﷺ challenged his assumption about the man's intention:
أَفَلَا شَقَقْتَ عَنْ قَلْبِهِ حَتَّى تَعْلَمَ أَقَالَهَا أَمْ لَا؟
Did you open his heart to know whether he said it sincerely or not? (Sahih Muslim)
A person cannot claim certain knowledge of another's hidden conviction. Outward profession governs earthly treatment; the true state of the heart is known to Allah.
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Ahl al-Qibla, Sin and Faith, the Essence of Faith and Degrees of Believers
On one occasion in battle, Usama ibn Zayd killed a man who had uttered the testimony of faith. The Messenger ﷺ challenged his assumption about the man's intention:
أَفَلَا شَقَقْتَ عَنْ قَلْبِهِ حَتَّى تَعْلَمَ أَقَالَهَا أَمْ لَا؟
Did you open his heart to know whether he said it sincerely or not? (Sahih Muslim)
A person cannot claim certain knowledge of another's hidden conviction. Outward profession governs earthly treatment; the true state of the heart is known to Allah.