One suffers from intermediate drops of urine, such that if he prays standing, the urine flows, and if he prays sitting the urine cedes. So, should he pray standing or sitting? There are two opinions. The relied-upon position [al-asahh] is sitting, to preserve purification; and there is no make-up due. (Rawdat al-Talibin 1/139)

And, Allah knows best.

Shafiifiqh.com Fatwa Dept.