Iyas reported on the authority of his father: I (had the honour of) leading the white mule on which rode Allah's Messenger (ﷺ) and with him were Hasan and Husain, till it reached the apartment of Allah's Messenger (ﷺ). The one amongst them was seated before him and the other one was seated behind him.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنِي عَبْدُ اللَّهِ بْنُ الرُّومِيِّ الْيَمَامِيُّ، وَعَبَّاسُ بْنُ عَبْدِ الْعَظِيمِ الْعَنْبَرِيُّ، قَالاَ حَدَّثَنَا النَّضْرُ بْنُ مُحَمَّدٍ، حَدَّثَنَا عِكْرِمَةُ، - وَهُوَ ابْنُ عَمَّارٍ - حَدَّثَنَا إِيَاسٌ، عَنْ أَبِيهِ، قَالَ لَقَدْ قُدْتُ بِنَبِيِّ اللَّهِ صلى الله عليه وسلم وَالْحَسَنِ وَالْحُسَيْنِ بَغْلَتَهُ الشَّهْبَاءَ حَتَّى أَدْخَلْتُهُمْ حُجْرَةَ النَّبِيِّ صلى الله عليه وسلم هَذَا قُدَّامَهُ وَهَذَا خَلْفَهُ .
sunnah.com