The difference between say and tell is quite known. Most of the grammar sites/books make it very clear and I understand this topic.
Usage rules for Tell and Say
Tell is used only to instruct or inform, and when the receiver of the information is included as an object of the verb. Do not use for quotes.
Has she told you the good news, yet?
Please tell us your name and occupation.
The police officer told him to stop. [NOT The police offer told him, "Stop."]
Can you tell me what happened?
Now, when it comes to tell the truth I have read some instances where the object is NOT present.
Good people always tell the truth
Where is the object then? You always tell someone something. You never tell something. You say that.
Okay, so here is the quote I made and always tell (to!) others. Which version is better and grammatical?:
You should tell the truth to those who deserve it OR
You should tell those the truth who deserve it
If I go by books then the latter one seems correct - you tell someone something because we know she told me what was happening over she told to me what was happening.