Question:

I was fasting yesterday, then I forgot to pray Asr prayer as I got carried away with lectures, by the time I remembered it was some minutes to maghrib prayer, when I went to perform I saw that my period had started. How am I supposed to pray that salah and is my fast valid?

Answer:

Bismillahi Taʿālā

Assalāmu ʿalaykum waraḥmatullāhī wabrakātuh,

Menstruation starts during a particular Ṣalāh time

It is mentioned in “Heavenly Ornaments”:

If she begins to bleed at the end of a Ṣalāh time and had not offered her Ṣalāh as yet, even then she is excused from that Ṣalāh.

Since you had not performed your ʿAṣr as yet, and you noticed that your bleeding started before Maghrib could commence, you are excused from performing your ʿAṣr Ṣalāh. Even when your menstruation finishes, you do not need to make qaḍāʾ of this ʿAṣr.

Menstruation starts while fasting

Heavenly Ornaments mentions:

If she begins to bleed while fasting, that fast will break and she will have to make qaḍāʾ of it. Even if she bleeds while keeping an optional fast, she will have to make qaḍāʾ of it.

Your optional fast was invalidated by the bleeding before it could be completed. Hence qaḍāʾ has become wājib upon you. Once your menstruation has finished, you may keep a qaḍāʾ fast to compensate for this one.

And Allāh Taʿālā knows best,

Wassalamu ʿalaykum,

Mufti Faisal al-Mahmudi

الدر المختار وحاشية ابن عابدين – دار الفكر (1/ 291)
(قوله ولو شرعت تطوعا فيهما) أي في الصلاة والصوم؛ أما الفرض ففي الصوم تقضيه دون الصلاة وإن مضى من الوقت ما يمكنها أداؤها فيه؛ لأن العبرة عندنا لآخر الوقت