Prayer: What Should One Do After Janābah in a Masjid If Unable to Leave Immediately?

Practical Laws of Islam as per the teachings of Imam Khamenei

Prayer: What Should One Do After Janābah in a Masjid If Unable to Leave Immediately?

Question #420:

What is the duty of someone who enters a masjid at night, sleeps there, and has a nocturnal emission but cannot leave the masjid after he wakes up?

Answer #420:

If there is no way that he can leave the masjid and go to somewhere else, it is obligatory for him to perform tayammum at once which makes it permissible for him to remain in the masjid.

-Imam Khamenei, Practical Laws of Islam, Importance and Conditions of Prayer