1Being told not to worry has never once stopped anybody worrying, including you. If a friend said it to you tomorrow you would carry straight on.
This is worth saying to a parent who feels they are failing at comforting their child. They are not bad at it. The words simply do not do that job for anyone. What does help is staying nearby, taking the fear seriously enough to hear it once, and then going on with the evening rather than negotiating with it.
Islamic evidence
I am near. I respond to those who call Me (Quran 2:186). What is offered is nearness and a response, not a promise that nothing will go wrong.
“[Prophet], if My servants ask you about Me, I am near. I respond to those who call Me, so let them respond to Me, and believe in Me, so that they may be guided”
Qur'an 2:186
Psychological evidence
A pilot randomised trial in 20 outpatients compared metacognitive therapy, which works on a person's beliefs about worrying rather than on the worries themselves, with applied relaxation, and it came out well with nobody dropping out. The interesting part is where it aimed. It was a very small pilot, so it points a direction rather than settling anything.
Wells A, Welford M, King P, Papageorgiou C, Wisely J, Mendel E. (2010). Behaviour research and therapy · doi
Review detail
Why it works. Comforting words aim at the content of a worry, which is not the part that keeps it running.