It is narrated from Sayyiduna Abu Umamah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "I have been favoured with four things: the earth has been made a place of prayer and a means of purification for me, so whichever man of my Ummah reaches the time of prayer and does not find water, let him regard the earth as a place of prayer and a means of ablution; I have been sent to all people; I have been helped by awe from a month's journey, which goes ahead of me; and the spoils of war have been made lawful for me."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1019