Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.042B.

Said Buraidah, “The Prophet, upon whom be peace, made ablution for every prayer. On the day of the conquest of Makkah, he made ablution, wiped over his socks and prayed a number of times with just one ablution. ‘Umar said to him, ‘O Messenger of Allah, you did something that you have not done (before).’ He answered, ‘I did it on purpose, ‘Umar.”‘ (Related by Ahmad, Muslim and others.)

Said Anas ibn Malik, “The Prophet, upon whom be peace, used to make ablution for every prayer.” He was asked, “And what did you people use to do?” Malik said, “We prayed the prayers with one ablution unless we nullified it.” (Related by Ahmad and al-Bukhari.)

Abu Hurairah reported that the Prophet said, “Were it not to be a hardship on my people, I would order them to make ablution for every prayer.” (Related by Ahmad with a hassan chain.)

Ibn ‘Umar reported that the Prophet, upon whom be peace, said, “Whoever makes ablution while he is already in a state of purity will have ten good deeds written for him.” (Related by Abu Dawud, at-Tirmizhi, and Ibn Majah.)