https://abukhadeejah.com/why-did-the-prophet-salallahu-alaihi-wasallam-not-sleep-before-isha-and-not-stay-awake-after-it-%e2%80%95shaikh-salih-al-fawzan/
Why did the Prophet (salallāhu 'alaihi wasallam) not sleep before 'Ishā and not stay awake after it? ―Shaikh Sālih Al-Fawzān