The Prophet ﷺ said, "Do not let the bedouins overcome you regarding the name of your prayer. It is al-Isha, but they call it al-atamah because they delay milking their camels until late at night."
حدثنا سفيان عن ابن أبي لبيد عن أبي سلمة سمعت
عن النبي ﷺ قال لا تغلبنكم الأعراب على اسم صلاتكم ألا وإنها العشاء وإنهم يعتمون بالإبل أو عن الإبل
Its isnad is sahih. Muslim, Nasai, and Ibn Majah also narrated it, as noted in al-Muntaqa 589.Yatimun: In al-Nihayah, Azhari said, "Livestock owners in the desert graze their camels, then have their evening meal at the place where the animals are penned, until they yaatimun, meaning they enter the atmah of the night, which is its darkness. The bedouin used to call the isha prayer 'the prayer of atmah,' naming it after its time. So the Prophet forbade them from following that practice, and preferred that they hold to the name given by the language of the sharia."