"The Messenger of Allah ﷺ used to accept the invitation of a slave."
سَمِعَ أَنَسَ بْنَ مَالِكٍ يَقُولُ كَانَ رَسُولُ اللَّهِ ﷺ يُجِيبُ دَعْوَةَ الْمَمْلُوكِ
This hadith has been reported on the authority of Anas through another chain of transmitters.
سَمِعْتُ أَنَسَ بْنَ مَالِكٍ يَقُولُ مِثْلَ ذَلِكَ
[Machine] He heard Anas ibn Malik saying, "The Prophet ﷺ would walk behind him, place his food on the ground, respond to the call of the slave, and ride a donkey."
أَنَّهُ سَمِعَ أَنَسَ بْنَ مَالِكٍ يَقُولُ «كَانَ النَّبِيُّ ﷺ يُرْدِفُ خَلْفَهُ وَيَضَعُ طَعَامَهُ فِي الْأَرْضِ وَيُجِيبُ دَعْوَةَ الْمَمْلُوكِ وَيَرْكَبُ الْحِمَارَ»