Upon completing the ablution › Wudu & Purification
Dua after ablution — testimony of faith
أَشْـهَدُ أَنْ لاَ إِلَـهَ إِلاَّ اللَّــهُ وَحْـدَهُ لَا شَرِيـكَ لَـهُ
وَأَشْهَدُ أَنَّ مُحَمَّـداً عَبْــدُهُ وَرَسُـوْلُـه
Ashhadu an lā ilāha illallāhu waḥdahu lā sharīka lah, wa ashhadu anna Muḥammadan ʿabduhu wa rasūluh.
Translation
I bear witness that none has the right to be worshipped except Allah, alone without partner, and I bear witness that Muhammad is His slave and Messenger.
When to recite
Upon completing ablution (wudu).
Source / Reference
Hisnul Muslim 13