All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
If the person wakes up and knows that if he performs Istinjaa’ and ablution, urine would come out during the ablution, then he should wait until he is certain that the urine has stopped. If he knows that if he waits until the urine stops, he would miss the prayer, then his ruling is that of the person suffering from incontinence. He should perform ablution and the prayer, even if urine still comes out, and it does not invalidate his prayer.
The person suffering urinary incontinence is like the woman suffering Istihaadhah (bleeding outside menstrual period). Ibn Qudaamah said, “If the woman experiencing Istihaadhah knows that the blood flow usually ceases for a period of time sufficient to perform ablution and prayer, then she should not perform the prayer during the blood flow and she should wait until it stops. If she fears missing the prayer, then she should perform ablution and pray (regardless of the blood flow).” [Al-Mughni]
Allah knows best.