I experienced menstrual pain before noon, but I did not start bleeding and the Thuhr prayer became due. I delayed the Thuhr Prayer until 1pm and, when I went to perform the prayer, I found that the bleeding had started. Is it a sin that I had delayed the Thuhr prayer that way? Am I to be blamed for delaying the prayer in such a case?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

As long as the bleeding did not start except during the time of the Thuhr prayer when you are allowed to delay it, then you are exempted from making up for that prayer. This is because the excuse that releases you from this obligation occurred during the time of the Thuhr prayer.

The evidence for this is what Abu Hurayrah narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever could catch one Rak‘ah (of the Fajr prayer) before sunrise, has  caught the (morning) prayer and whoever could catch one Rak‘ah of the ‘Asr prayer before sunset, has  caught the (‘Asr) prayer." [Al-Bukhari and Muslim]

This indicates that if one managed to perform only one Rak‘ah of the prayer before its time ends, he performed the prayer in its time. If the bleeding starts while there is enough time to perform one Rak‘ah of the prayer before its time ends, you are excused, released from that obligation and do not have to make up for that prayer.

However, you should have hastened to perform the prayer at the beginning of its time if you are expecting menstruation. You should only repent from your being not prompt in performing the prayer in its due time, but you are not obliged to make it up.