Serving the Deity

Do not flatter people before the Deity

Let the Lord be the only one praised in His presence. Do not praise or flatter other people there.

In the temple room, praise belongs to the Deity. Eulogizing another person there, however deserving, turns the attention away from the Lord. The Nectar of Devotion lists praising others before the Deity among the offenses to avoid. You can thank and appreciate people warmly outside.

Whose teaching
Vedic scripture
Where it is taught
The Nectar of Devotion, ch. 8: offense 21
Source
Vedabase