مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4281
Musnad of Abdullah bin Mas'ood
It was narrated that 'Abdullah said: The Messenger of Allah (ﷺ) said: No one will enter Paradise in whose heart is pride the size of a mustard seed.
Musnad Ahmad 4310A saheeh Hadeeth, Muslim (91)]