Someone said that supplication made at the first sighting of the Kaaba is always granted. Is there any truth to this?

Praise be to Allaah. 

This is not true; there has to be evidence (daleel)
for this to be true, because acts of worship should only be based on
evidence. And that evidence must be saheeh in and of itself and it should
be clear and unambiguous. And Allaah knows best.