What is the ruling on a husband having intercourse with his wife after her menstruation has ceased but before she has performed ghusl, based on his command to her to perform tayammum?

It is obligatory to perform a ritual bath (ghusl) if water is available and one is able to use it, based on the Almighty's saying: "So when they have purified themselves, then come to them from where Allah has ordered you." However, in cases of travel, or illness that prevents the use of water, or the absence of water, then tayammum (dry ablution) suffices.