If the debtor is unable to pay, wait for a better time. If you give up the loan as a charity, it would be better for you, if you only knew.
وَإِن كانَ ذو عُسرَةٍ فَنَظِرَةٌ إِلىٰ مَيسَرَةٍ وَأَن تَصَدَّقوا خَيرٌ لَكُم إِن كُنتُم تَعلَمونَ
wa in kaana zoo ‘usratin fanaziratun ilaa maisarah; wa an tasaddaqoo khairul lakum in kuntum ta’lamoon