Salatul Ijara is hiring someone to offer the qadha salaa* for a marhum/marhuma with payment. The person may also be paid for performing the qadha sawm and hajj.

If a person did not pray some of his wajib salaa, and did not perform their qadha, in spite of being able to do so, after his death, it is upon his eldest son, as ihtiyate wajib to perform the qadha. If the son cannot do so, he may hire someone to perform them. The qadha salaa of a mother are not wajib upon the eldest son – however, it is better if he performs them.

If a person makes a wasiyya (will) that all his/her qadha wajibaat must be performed, then it is the responsibility of the executor of his/her will to ensure that the qadha are performed.

*As long as a person is alive, no other person can offer his/her qadha on his/her behalf, even if he/she is unable to offer them.