Serving the Deity

Speak only truth and kindness before the Deity

Do not lie, scold, or speak harshly or insultingly to anyone in front of the Deity.

The Lord is present before you, so keep your words as clean as your clothes. The Nectar of Devotion warns against telling lies, scolding, speaking harshly and calling people insulting names before the Deity. If you are angry, step outside until it has passed.

Whose teaching
Vedic scripture
Where it is taught
The Nectar of Devotion, ch. 8: offenses 12, 17, 19 and 22
Source
Vedabase
Speak only truth and kindness before the Deity · HariHariBol