What is the Shar'i (Islamic legal) ruling on the tenant's termination of a rental contract after signing it, paying one month's rent in advance, receiving the apartment keys, and then wishing not to continue after four days of receiving them?

The lease is a binding contract, according to the majority of scholars. Neither party may unilaterally terminate it except with the consent of the other. The rent for the entire lease period is due in full from the lessee, even if he terminates the lease before its expiration and voluntarily relinquishes the benefit. It is recommended for the lessor to accept the lessee's request for rescission (iqalah), based on the Prophet's (peace be upon him) saying: "Whoever rescinds a Muslim's transaction, Allah will rescind his slip." The preponderant opinion is that iqalah is a rescission, not a sale, so it is not valid with an increase in price. If you agree to the rescission, then it is not permissible to take the full amount of the prepaid month, but only the portion corresponding to the days the lessee benefited.