Praise be to Allaah.
Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him) said: “Saying ‘May you live forever’ is a kind of transgression in du’aa’, because living forever is impossible and is contrary to what Allaah says. Allaah says (interpretation of the meaning):
“Whatsoever is on it (the earth) will perish.And the Face of your Lord full of Majesty and Honour will remain forever”
“And We granted not to any human being immortality before you (O Muhammad); then if you die, would they live forever?”
From Majmoo’ Fataawa Ibn ‘Uthaymeen (may Allaah have mercy on him), 3/69.