A boy belonging to a poor family cut off the ear of a boy belonging to a wealthy family. The family of the poor boy came to the Prophet ﷺ and said, "Prophet of Allah, we are poor people."So he did not impose anything upon him.
حدثنا معاذ بن هشام حدثني أبي عن قتادة عن أبي نضرة
أن غلاما لأناس فقراء قطع أذن غلام لأناس أغنياء فأتى أهله النبي ﷺ فقالوا يا نبي الله إنا ناس فقراء فلم يجعل عليه شيئا
Its isnad is sahih. It is found in Abu Dawud 4/196, no. 4590, in the chapter on blood money, "The offense of a slave falls upon the poor." Bayhaqi 8/105 has something similar. And in similar wording, Nasai 8/25, no. 4751, in the chapter on qasamah, "The waiving of retaliation among slaves." And Darimi 2/254, no. 2368, in the chapter on blood money, "Retaliation between two slaves."