Sahl said, "Al-Mundhir ibn Abi Usayd was brought to the Prophet ﷺ when he was born and the Prophet placed him on his thigh while Abu Usayd was seated near him. The Prophet ﷺ was busy with something in front of him, so Abu Usayd told someone to take his son from the Prophet's leg. When the Prophet ﷺ became aware of it, he asked, 'Where is the child?' Abu Usayd replied, 'We sent him home.' The Prophet asked, 'What is his name?' He replied, 'Such-and-such.' The Prophet said, 'No, rather his name is al-Mundhir.' So we called him al-Mundhir from that day."

عَنْ سَهْلٍ قَالَ أُتِيَ بِالْمُنْذِرِ بْنِ أَبِي أُسَيْدٍ إِلَى النَّبِيِّ ﷺ حِينَ وُلِدَ فَوَضَعَهُ عَلَى فَخِذِهِ وَأَبُو أُسَيْدٍ جَالِسٌ فَلَهَى النَّبِيُّ ﷺ بِشَيْءٍ بَيْنَ يَدَيْهِ وَأَمَرَ أَبُو أُسَيْدٍ بِابْنِهِ فَاحْتُمِلَ مِنْ فَخِذِ النَّبِيِّ ﷺ فَاسْتَفَاقَ النَّبِيُّ ﷺ فَقَالَ أَيْنَ الصَّبِيُّ؟ فَقَالَ أَبُو أُسَيْدٍ قَلَبْنَاهُ يَا رَسُولَ اللهِ قَالَ مَا اسْمُهُ؟ قَالَ فُلاَنٌ قَالَ لاَ لَكِنِ اسْمُهُ الْمُنْذِرُ فَسَمَّاهُ يَوْمَئِذٍ الْمُنْذِرَ