Yes,it is not only permissible but sometimes it is necessary to maintain steadfastness during tribulations which are usually expected in our life in this world.[sabr] patience,is so important in our life that it came in the Hadeeth:The status of patience from the iman is like the status of the head from the body.even in Quran there are many verses mentioning the great results of patience [indeed the patient believers will get their reward without counting].Az-zumar{39}
wassalam.