مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3280
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn '‘Abbas (رضي الله عنه) said: al-Aqra`bin Habis asked The Messenger of Allah (ﷺ): Messenger of Allah, is Hajj only once or is it every year? He said: "No, rather it is once, and whoever does more, it is voluntary.”
Musnad Ahmad 3303A saheeh hadeeth]