مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3888
Musnad of Abdullah bin Mas'ood
It was narrated that ‘Abdullah (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: "No one in whose heart is pride the size of a grain will enter Paradise, and no one in whose heart is faith the size of a mustard seed will enter Hell."
Musnad Ahmad 3913Its isnad is saheeh, Muslim (91)]