Is it obligatory for the one afflicted with سلس (incontinence) to perform istinja' (ablution with water) for every prayer after the time for it has begun, or can he perform istinja' and wudu' (ritual ablution) a little before the time begins?

The person in a state of perpetual ritual impurity ( صاحب الحدث الدائم ) performs ablution after the time for prayer begins. He should precede ablution with istinja' (washing the private parts). The Shafi'is and Hanbalis stipulate that there must be an immediate succession (muwalat) between istinja' and taking precautionary measures (tahaffuz), between the actions of ablution, and between ablution and prayer. He must also take precautions and tighten whatever prevents the discharge of the impurity.