Matar (al-Warraq) narrated that I asked Hasan and Ata’ (may Allah have mercy on them) about a man who is traveling with his wife, and she gets her menses, then becomes pure but does not find water. Both of them said: She should perform tayammum and pray. Matar said: Can her husband have intercourse with her in this state? They replied: Prayer is greater than that. That is, if she can pray, then she can also be intimate with her husband.
Hadith Referenceسنن دارمي / من كتاب الطهارة / 1209