مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4339
Musnad of Abdullah bin Mas'ood
It was narrated from Mansoor... And he narrated it with its isnad and a similar meaning. And he said: The Messenger of Allah (ﷺ) smiled so broadly in approval of what he said that his molars appeared.
Musnad Ahmad 4369lts isnad is saheeh, al-Bukhari (7414)]