Conditions for the validity of Salaah

Joining two Salaahs in one time

Q: Please advise on the ruling regarding joining of Salaahs when one is a musaafir. Most people join their salaah saying it is permitted as a musafir and better to join than miss it. And in which circumstances will it be permissible to join? If a person joins their Salaah regularly as a musafir will the salaah be valid?

When does Tahajjud time end?

Q: I have two questions which I kindly request you to answer me.

1. I have doubt regarding tahajjud Salaah. I want to know when it exactly ends. Say the fajr Salaah starts at 5.23 am in where I live , now. Till wheat time then can we pray tahajjud Salaah? I want to know the timing so I can rectify if I make any mistakes.

2. Can we recite salawatun naariya with a particular niyat to be fulfilled? Where I live people recite it 4444 times with a particular niyat he or she has. Is it permissible?