Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said, “Do not refer to anyone as ‘my slave,’ for all of you are the slaves of Allah. Rather, you should refer to him as ‘my young man.’ The servant should not refer to anyone as ‘my lord,’ but rather he should refer to him as ‘my master.’”
Source: Ṣaḥīḥ Muslim 2249
Grade: Sahih (authentic) according to Muslim
عَنْ أَبِي هُرَيْرَةَ قَالَ قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ لَا يَقُولَنَّ أَحَدُكُمْ عَبْدِي فَكُلُّكُمْ عَبِيدُ اللَّهِ وَلَكِنْ لِيَقُلْ فَتَايَ وَلَا يَقُلْ الْعَبْدُ رَبِّي وَلَكِنْ لِيَقُلْ سَيِّدِي
2249 صحيح مسلم كتاب الألفاظ من الأدب وغيرها باب حكم إطلاق لفظة العبد والأمة والمولى والسيد