مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2647
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated from Ibn ‘Abbas (رضي الله عنه) that the Prophet (ﷺ) said: "Every Muslim must do Hajj, and if I said (it should be done) every year, it would be (obligatory)."
Musnad Ahmad 2663A saheeh hadeeth; this is a da'eef isnad]