Can a person shorten his prayer
    before leaving his city?
Question

                A man sets out from his house as a
      traveller, then the time for ‘Asr comes before he has left the city or the area where
      he is. Should he shorten his prayer or pray it in full?
Praise be to Allah.If the time for prayer comes when the traveller is still in his city,
    then he should pray it in full because he has not yet left his city. If he has left his
    city and is on the road when the time for prayer comes, then he should pray two
    rak’ahs even if the adhaan came before he left his city. What counts here is the
    prayer (not the adhaan). Similarly, if the time for prayer comes whilst you are still
    travelling, but you reach your home before you pray, then you have to pray four
    rak’ahs, because in this case what counts is the actual prayer. If you pray when you
    are travelling, you should shorten your prayer; if you pray when you are at home, you
    should pray it in full.