It was narrated from 'Amr bin Shu'aib, from his father, from his grandfather, that: the Messenger of Allah (ﷺ) went to a camel, and took a hair from its hump between his fingers and said: "I am not entitled to take anything from the Fay, not even this, except the Khumus, and the Khumus will come back to you."
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا عَمْرُو بْنُ يَزِيدَ، قَالَ حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، قَالَ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ مُحَمَّدِ بْنِ إِسْحَاقَ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم أَتَى بَعِيرًا فَأَخَذَ مِنْ سَنَامِهِ وَبَرَةً بَيْنَ إِصْبَعَيْهِ ثُمَّ قَالَ " إِنَّهُ لَيْسَ لِي مِنَ الْفَىْءِ شَىْءٌ وَلاَ هَذِهِ إِلاَّ الْخُمُسُ وَالْخُمُسُ مَرْدُودٌ فِيكُمْ " .
sunnah.com