Jabir said, "One of our men had a son and named him al-Qasim. The Ansar said, "We will not give you the kunya of Abu'l-Qasim to make you happy.' He went to the Prophet, may Allah bless him and grant him peace, and told him what the Ansar had said. The Prophet, may Allah bless him and grant him peace, said, 'The Ansar did well. Call yourselves with my name but do not use my kunya. I am Qasim (the divider)."
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ يُوسُفَ، قَالَ: حَدَّثَنَا سُفْيَانُ، عَنِ الأَعْمَشِ، عَنْ سَالِمِ بْنِ أَبِي الْجَعْدِ، عَنْ جَابِرٍ قَالَ: وُلِدَ لِرَجُلٍ مِنَّا غُلاَمٌ فَسَمَّاهُ الْقَاسِمَ، فَقَالَتِ الأَنْصَارُ: لاَ نُكَنِّيكَ أَبَا الْقَاسِمِ، وَلاَ نُنْعِمُكَ عَيْنًا، فَأَتَى النَّبِيَّ صلى الله عليه وسلم فَقَالَ لَهُ: مَا قَالَتِ الأَنْصَارُ، فَقَالَ النَّبِيُّ صلى الله عليه وسلم: أَحْسَنَتِ الأَنْصَارُ، تَسَمُّوا بِاسْمِي، وَلاَ تَكْتَنُوا بِكُنْيَتِي، فَإِنَّمَا أَنَا قَاسِمٌ.
sunnah.com