'Abdullah bin 'Amr bin Al-'As (May Allah be pleased with them) reported:
The Messenger of Allah ﷺ said, "Allah forgives every sin of a martyr, except his debt."

[Muslim].

Another narration in Muslim is: The Messenger of Allah ﷺ said, "Being martyred in the Cause of Allah expiates for everything, except debt."

وعن عبد الله بن عمرو بن العاص رضي الله عنهما أن رسول الله ﷺ قال: "يغفر الله للشهيد كل شيء إلا الدين" ((رواه مسلم)).