Is it permissible for men to pray behind women in the Grand Mosque, and what is the reason for that?

The prayer of men behind rows of women is valid according to the majority of scholars, though it is disliked (makrooh). The Sunnah is for men to be in front and women's rows to be behind. This does not invalidate the prayer due to lack of evidence. The Grand Mosque (Masjid al-Haram) is like any other mosque in this ruling, but due to the intense crowding, especially during circumambulation (tawaf), this situation may occur frequently. A Muslim should strive not to pray behind women if possible, and women should not have their rows in front of men. If there is no alternative, then there is no harm, and the prayer is valid, God willing, because hardship brings ease.