"I heard the Messenger of Allah say: 'Do not let the Bedouin make you change the name of your prayer. It is the 'Isha', and they bring their camels in and milk them at nightfall.'"  

سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ لاَ تَغْلِبَنَّكُمُ الأَعْرَابُ عَلَى اسْمِ صَلاَتِكُمْ فَإِنَّهَا الْعِشَاءُ وَإِنَّهُمْ لَيُعْتِمُونَ بِالإِبِلِ  

The Prophet said: "Do not let the Bedouins make you change the name of your prayer." Ibn Harmalah added: "Rather it is the 'Isha', but they say the 'Atamah because they bring their camels in for milking at that time (when it is dark)."  

أَنَّ النَّبِيَّ ﷺ قَالَ لاَ تَغْلِبَنَّكُمُ الأَعْرَابُ عَلَى اسْمِ صَلاَتِكُمْ زَادَ ابْنُ حَرْمَلَةَ فَإِنَّمَا هِيَ الْعِشَاءُ وَإِنَّمَا يَقُولُونَ الْعَتَمَةُ لإِعْتَامِهِمْ بِالإِبِلِ