Question posed to Shaykh Saalih al-Fawzaan (may Allaah preserve him):
If the time of Salaatul-‘Eshaa comes in, however the woman doesn’t pray it in the beginning of its time, rather she delays it until the middle of its time, then she further delays it until the end of its time and then her monthly cycle comes all of a sudden–is it upon her to make up that obligatory pray which she delayed after she becomes clean from her menses or not? Also what is the ruling if the opposite was to happen? She becomes clean from her menses and the time of the obligatory Salaah from one of the five obligatory prayers is still in. Does she pray or not?
If the woman reaches (the time of) prayer from one of the (five) prayers, and she didn’t perform it until her menses came upon her, indeed it is obligatory upon her to pray that prayer whose time reached her (that she didn’t pray when she was clean from her menses) when her menses leaves and she becomes clean. That’s because the prayer became obligatory upon her by way of the time of the prayer entering (while she was in a state of purity from her menses). And likewise the opposite. If the woman becomes clean from her menses during the end of the time of the prayer, it is obligatory upon her to make ghusl and pray this prayer. Also it is upon her to pray the prayer that’s before it, that can be combined with it. Like if she was to become clean at the end of the time of Salaatul-‘Asr, she is to pray ath-Thuhr and al-‘Asr. Also whoever becomes clean (from the menses) at the end of the time for Salaatul-‘Eshaa, then she is to prayer al-Maghrib and al-‘Eshaa.
Silsilah al-Muntaqaa min Fataawaa al-‘Allaamah Saalih al-Fawzaan, Kitaabut-Tahaarah pg. 77