It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) used to perform a fresh ablution for every prayer, while (the earlier) ablution sufficed us as long as we did not break it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 761