Abu Umamah ؓ reported: Abu Dharr ؓ reproached Bilal ؓ about his mother, saying, “O son of a black woman!” Bilal ؓ went to the Messenger of Allah ﷺ and he told him what he said. The Prophet ﷺ became angry and then Abu Dharr ؓ came, although he was unaware of what Bilal ؓ told him. The Prophet ﷺ turned away from him and Abu Dharr ؓ asked, “O Messenger of Allah ﷺ, have you turned away because of something you have been told?” The Prophet ﷺ said:

أَنْتَ الَّذِي تُعَيِّرُ بِلالا بِأُمِّهِ وَالَّذِي أَنْزَلَ الْكِتَابَ عَلَى مُحَمَّدٍ مَا لأَحَدٍ عَلَيَّ فَضْلٌ إِلا بِعَمَلٍ إِنْ أَنْتُمْ إِلا كَطَفِّ الصَّاعِ

Have you reproached Bilal ؓ about his mother? By the one who revealed the Book to Muhammad ﷺ, none is more virtuous over another except by righteous deeds. You have none but an insignificant amount.

Source: Shu’b al-Iman 4760, Grade: Sahih