What is the ruling on performing ablution while already in a state of ablution?

Renewing ablution (performing ablution over an existing ablution) is considered desirable by the majority of jurists, including the four Imams, with varying conditions for each madhhab. They have cited several hadiths as evidence, among them: "Whoever performs ablution over purity, he will have ten good deeds" (weak), and "The Messenger of Allah, peace and blessings be upon him, used to perform ablution for every prayer," and "Ablution over ablution is light upon light" (weak), and what was narrated from Buraydah that the Prophet, peace and blessings be upon him, prayed the obligatory prayers with a single ablution on the day of the Conquest [of Mecca] to show its permissibility. Furthermore, Ash-Shawkani holds that the hadiths regarding the virtue of ablution indicate its desirability.