Is It Necessary to Renew Wudu before Sleeping?
Question

About the Hadeeth of the Prophet (PBUH) how we would make his Wudu for prayer before sleeping, if I still have Wudu for Salat Al-Ishaa, can I go to sleep with this Waduu, or should I do it again before I sleep?
Praise be to Allah.Doing Wudu before going to sleep is one of the things which is recommended to do before going to sleep. 
A Hadith was narrated to this effect, in which the Prophet (peace and blessings of Allah be upon him) said: “When you go to bed, do Wudu as for prayer.” (Narrated by Al-Bukhari, 247; Muslim 2710) 
Ibn Hajar said: “The apparent meaning is that it is recommended for everyone who wants to go to sleep to renew his Wudu, even if he already has Wudu. It may be interpreted as applying only to the one who has broken his Wudu.” 
An-Nawawi said: “If a person has Wudu, that is sufficient for him, because the point is to go to sleep having Wudu, lest he die in his sleep, and so that his dreams will be more true, and so that the Shaytan will be less likely to play with his dreams and terrify him.”
For more details, please refer to these answers: 21647 , 2063 , 96589 , 30784 , 14033 , and 5287 .           
And Allah knows best.