Is it necessary to renew ablution (wudu') that has been nullified before sleeping in order to attain the Sunnah of the Prophet, peace be upon him?

It is recommended to sleep in a state of ritual purity (tahara). If one's ablution (wudu) is nullified before sleeping, it is desirable to renew it in order to achieve sleep in a state of purity. It is held that if one performs ablution and then lies down, there is no obligation to renew the ablution if one wakes up for some need, as the Sunnah has been fulfilled by the initial ablution.