When Al-Mundhir bin Abu Usaid was born, he was brought to the Prophet ﷺ who placed him on his thigh. While Abu Usaid was sitting there, the Prophet ﷺ was busy with something in his hands so Abu Usaid told someone to take his son from the thigh of the Prophet ﷺ . When the Prophet ﷺ finished his job (with which he was busy), he said, "Where is the boy?" Abu Usaid replied, "We have sent him home." The Prophet ﷺ said, "What is his name?" Abu Usaid said, "(His name is) so-and-so. " The Prophet ﷺ said, "No, his name is Al-Mundhir." So he called him Al-Mundhir from that day.  

أُتِيَ بِالْمُنْذِرِ بْنِ أَبِي أُسَيْدٍ إِلَى النَّبِيِّ ﷺ حِينَ وُلِدَ فَوَضَعَهُ عَلَى فَخِذِهِ وَأَبُو أُسَيْدٍ جَالِسٌ فَلَهَا النَّبِيُّ ﷺ بِشَىْءٍ بَيْنَ يَدَيْهِ فَأَمَرَ أَبُو أُسَيْدٍ بِابْنِهِ فَاحْتُمِلَ مِنْ فَخِذِ النَّبِيِّ ﷺ فَاسْتَفَاقَ النَّبِيُّ ﷺ فَقَالَ أَيْنَ الصَّبِيُّ فَقَالَ أَبُو أُسَيْدٍ قَلَبْنَاهُ يَا رَسُولَ اللَّهِ قَالَ مَا اسْمُهُ قَالَ فُلاَنٌ قَالَ وَلَكِنْ أَسْمِهِ الْمُنْذِرَ فَسَمَّاهُ يَوْمَئِذٍ الْمُنْذِرَ  

Zainab's original name was "Barrah," but it was said' "By that she is giving herself the prestige of piety." So the Prophet ﷺ changed her name to Zainab.  

أَنَّ زَيْنَبَ كَانَ اسْمُهَا بَرَّةَ فَقِيلَ تُزَكِّي نَفْسَهَا فَسَمَّاهَا رَسُولُ اللَّهِ ﷺ زَيْنَبَ  

That when his grandfather, Hazn visited the Prophet ﷺ the Prophet ﷺ said (to him), "What is your name?" He said, "My name is Hazn." The Prophet ﷺ said, " But you are Sahl." He said, "I will not change my name with which my father named me." Ibn Al-Musaiyab added: So we have had roughness (in character) ever since.  

فَحَدَّثَنِي أَنَّ جَدَّهُ حَزْنًا قَدِمَ عَلَى النَّبِيِّ ﷺ فَقَالَ مَا اسْمُكَ قَالَ اسْمِي حَزْنٌ قَالَ بَلْ أَنْتَ سَهْلٌ قَالَ مَا أَنَا بِمُغَيِّرٍ اسْمًا سَمَّانِيهِ أَبِي قَالَ ابْنُ الْمُسَيَّبِ فَمَا زَالَتْ فِينَا الْحُزُونَةُ بَعْدُ