All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
A group of scholars are of the view that a tiny impurity is overlooked, like a drop of urine, and that it is not an obligation to wash it if it is difficult to avoid it. Moreover, some of them are of the view that impurity is overlooked even if it is too much when it is difficult to purify it; this is the view of the Maaliki School.
Therefore, according to this view, if it is difficult to avoid the urine which stains your clothes, and it is difficult for you to change them or wash them, then it is permissible for you to perform the prayer with it; Islam is an easy religion. Allaah Says (what means): {…and has not placed upon you in the religion any difficulty.}[Quran 22:78] However, if it is not difficult to avoid the impurity or that there is no hardship to clean your clothes or change them, then it is not permissible to perform the prayer while there is an impurity in your clothes. For the prayer to be valid, it is a condition that the body, clothes and place should be pure.
As regards combining the prayers because of incontinence of urine, then the view which is adopted here in Islamweb is that combining the prayers is permissible for a person who has incontinence of urine, and that he has the choice either to perform them at the time of the first prayer or at the time of the second prayer. He should act according to what suits him, exactly like a sick person, as he is considered like him.
For more benefit, please refer to Fatwa 84463.
A person who has incontinence of urine and the like, may combine the prayers as follows: to combine (Thuhr and 'Asr), and (Maghrib and 'Ishaa’) prayers; this is to perform the first prayer at its ending time and the second prayer at its beginning time, so they are combined in form but not in reality, as each prayer is performed at its prescribed fixed time. This method of combining is more appropriate for those who are permitted to combine their prayers.
For more benefit, please refer to Fatwa 85661.
Allaah Knows best.