Should one perform ablution anew to recite the supplication for sleep, after returning from Fajr prayer and sleeping?

The Sunnah restricts the remembrances (adhkar) of sleep, and among them is the remembrance mentioned concerning night sleep, as it was reported in the two Sahihs and other collections, such as the hadith of Al-Bara bin Azib, Ali, and Mu'adh, may Allah be pleased with them. It is recommended to perform ablution (wudu') before sleeping, but it is not obligatory. It is sufficient for a person to sleep in a state of ritual purity, even if he had performed ablution earlier.