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.

Reference: Bukhari: 2662