451. Etiquette of praising a fellow Muslim
The Prophet (ﷺ) said: "Whoever amongst you has to praise his brother should say:
أَحْسِبُ فُلَانًا وَاللَّهُ حَسِيبُهُ وَلَا أُزَكِّي عَلَى اللَّهِ أَحَدًا أَحْسِبُهُ كَذَا وَكَذَا
Ahsibu fulaanan wAllaahu haseebuhu wa laa 'uzakkee 'alAllaahi 'ahadan ahsibuhu kadha wa kadha
I think that he is so and so, and Allah knows exactly the truth, and I do not confirm anybody's good conduct before Allah, but I think him so and so.
It is to be said when you must ensure you have knowledge that the certain characteristic is present in that person.
Related Duas:
For the one who asks Allah to forgive your sins
For the one that have been praised
If you see someone smiling
If anyone likes you for the sake of Allah
For one you have insulted
Protection from the Dajjal
If someone does a good job for you
Seeking refuge from four things
Forbiddance of ascribing things to omens
Dua to one who says 'May Allah bless you'