Amr bin Shu'ayb narrates from his grandfather (may Allah be pleased with him) that a man came to the Prophet (peace and blessings be upon him) and said: "If a man is in some distant place where there is no water, may he have intercourse with his wife?" He (peace and blessings be upon him) said: "Yes."
A report like this is strengthened by corroborating reports, and the hadith of Ammar bin Yasir and Imran bin Husayn, established from them both, corroborates these two.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1043