Mishkat al-Masabih

Abu Huraira reported God’s messenger as saying, “Shall I not guide you to something for which God blots out sins and raises men's ranks?” When his hearers expressed their desire that he should tell them, he said, “Performing complete ablution although circumstances make it difficult, travelling far to mosques, and looking expectantly to the next time of prayer after prayers have been said. That is the defence of the frontier.”