To the debtor when his debt is settled1 du'a

May Allah bless you in your family and your wealth, surely the reward for a loan is praise and retur...

Reference:An-Nasa'i, 'Amalul-Yawm wal-Laylahp. 300, Ibn Majah 2/809. See also Al-Albani, Sahih Ibn Majah2/55.Hisnul Muslim 202

بارَكَ اللهُ لَكَ في أَهْلِكَ وَمالِك إِنَّما جَـزاءُ السَّلَفِ الْحَمْدُ والأَداء

Transliteration

Bārakallāhu laka fī ahlika wa mālik. innamā jazā'us-salafi ‘l-ḥamdu wa‘l-adā'.

Translation

May Allah bless you in your family and your wealth, surely the reward for a loan is praise and returning (what was borrowed).