Is it permissible for a person with urinary incontinence to combine the Dhuhr and Asr prayers, and the Maghrib and Isha prayers, with a single ablution and a single Istinja, or is it obligatory to perform ablution and Istinja for each prayer despite the hardship?

It is permissible for someone with continuous urinary incontinence to combine two prayers (Dhuhr with Asr, and Maghrib with Isha) with a single ablution, whether it is an early combination (Jam' Taqdeem) or a delayed combination (Jam' Ta'kheer). This is by analogy with a woman experiencing prolonged non-menstrual bleeding (mustahadah) and others with valid excuses.