Purity: Sexual Intercourse When Unable to Perform Ghusl

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 352:

If someone cannot perform ghusl but can perform tayammum, he can still have sexual intercourse with his wife even after the time for prayers has set in.

-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)