Is it permissible to use a small amount of water for istinja’ and then perform tayammum, or is it obligatory to use istijmar and water for wudu’ for one who suffers from the obsessive thought of drops of urine escaping?

If you have a small amount of water that is insufficient for washing away urine and performing ablution (Wudu'), then:

- If the urine is not widespread such that it can be wiped away with a tissue, you should suffice with wiping and save the water for Wudu'.

- If the urine is widespread, then you must first remove it with water, and then perform Tayammum for prayer.

If you will find water for Wudu' before the prayer time expires, then use the water to remove the impurity. You are not required to repeat the prayer, whether you find the water before or after the time expires.