Salim (may Allah have mercy on him) heard al-Hasan (may Allah have mercy on him) say: There is no harm if the husband covers his wife (that is, has intercourse with her) while no water is available, they are on a journey, and the woman has become pure from menstruation, when she has only performed dry ablution (tayammum).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحيض / 1484