After doing ablution well, one should say:

أَشْهَدُ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَحْدَهُ لَا شَرِيْكَ لَهُ وَأَشْهَدُ أَنَّ مُحَمَّدًا عَبْدُهُ وَرَسُوْلُهُ

Ash-hadu 'an laa 'ilaaha 'illAllahu wahdahu laa shareeka lahu wa 'ash-hadu 'anna Muhammadan 'abduhu wa Rasooluhu

I bear witness that none has the right to be worshipped but Allah alone, Who has no partner; and I bear witness that Muhammad is His slave and His Messenger (ﷺ). Uqba bin 'Amir (RA) reported: Allah's Messenger (ﷺ) say: If any Muslim performs ablution well, then stands and prays two rak'ahs setting about them with his heart as well as his face, Paradise would be guaranteed to him.

Reference: Muslim: 234 , 576