Q: I was on safar (travel) and i went to a musjid. In the salah they read a dua. Is this an okay thing to do. For example, after ruku to just start reading a dua? (email)
A: Yes. Some mazhab take part in this action on a level of continuity as part of the Fajr Salah.
As for ahnaf, they can perform it at the time of calamity. Also, they should do it with a pause in between. For example, not every fajr every day. This dua is not too long for ahnaf and limited in its words and length with words derived from Hadith.
Rasulullah (SAW) read this dua when the sahaba were attacked. We too should recite this dua when innocent people are placed in unfair hardship.
Allah Certainly Knows Best.
Here is our example of this dua.