An Nasai: Hadith 537

"The Messenger of Allah (ﷺ) used to delay the later 'Isha'."[1] [1] It is described as the later 'Isha' prayer because the Maghrib prayer is sometimes called 'Isha' prayer, but it is the first 'Isha'. Some scholars are of the opinion that it is disliked to call Maghrib 'Isha' without qualifying it as the first 'Isha'. See Fath Al-Bari.