Hisnul Muslim 14

Upon completing the ablution

اَللَّهُـمَّ اجْعَلْنِـي مِنَ التَّـوَّابِينَ وَاجْعَـلْنِي مِنَ الْمُتَطَهِّـرِينَ

Allaahummaj'alnee minat-tawwaabeena waj'alnee minal-mutatahhireen.

O Allah, make me among those who turn to You in repentance, and make me among those who are purified.