I heard the Messenger of Allah ﷺ say, "Do not let the bedouins overcome you regarding the name of your prayer. It is indeed al-Isha, while they call it al-Atamah because they delay milking their camels until late."In another narration, "For in the Book of Allah it is called al-Isha, and they only call it al-Atamah because of their delay in milking the camels."
سمعت رسول الله ﷺ يقول: لا تغلبنكم الأعراب على اسم صلاتكم، ألا إنها العشاء، وهم يعتمون بالإبل. وفي رواية: فإنها في كتاب الله العشاء، وإنها تعتم بحلاب الإبل
Muslim reported it in the Book of Mosques (644) via Sufyan bin Uyayna, from Abu Labid, from Abu Salama, from Abdullah bin Umar, as mentioned above.His words, "yatimun" (they delay), mean they delay the milking of the camels, and they name the prayer after the time of milking. It is said, "So-and-so is skilled at hosting guests," when guests come to him and he does not delay serving them, as Khattabi stated in his commentary on Abu Dawud (5/261).His words, "its name in the Book of Allah is al-Isha," refer to His saying, "and after the isha prayer" [Nur 24:58]. However, the sahih hadiths mention calling it al-Atama, as in the hadith, "If they knew what is in the fajr and the atama prayers, they would come to them even if they had to crawl." And in the hadith of Abdullah bin Umar, the isha prayer is called al-atama, which is the hadith that follows.