Upon completing the ablution › Wudu & Purification
Dua after ablution — glorification and seeking forgiveness
سُبْحَـانَكَ اللَّهُـمَّ وَبِحَمْدِكَ
أَشْـهَدُ أَنْ لاَ إِلَهَ إِلاَّ أَنْــتَ أَسْــتَغْفِرُكَ وَأَتُـوْبُ إِلَـيْك
Subḥānaka Allāhumma wa biḥamdika, 'ash-hadu 'an lā 'ilāha 'illā 'Anta, 'astaghfiruka wa 'atūbu 'ilayk
Translation
How perfect You are O Allah, and I praise You, I bear witness that none has the right to be worshipped except You, I seek Your forgiveness and turn in repentance to You.
When to recite
Upon completing ablution (wudu).
Source / Reference
Hisnul Muslim 15