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)." (Using translation from Ibn Mājah 705)
عَنِ النَّبِيِّ ﷺ قَالَ لَا يَغْلِبَنَّكُمْ الْأَعْرَابُ عَلَى اسْمِ صَلَاتِكُمْ فَإِنَّهَا الْعِشَاءُ إِنَّمَا يَدْعُونَهَا الْعَتَمَةَ لِإِعْتَامِهِمْ بِالْإِبِلِ لِحِلَابِهَا