مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3253
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn ‘Abbas (رضي الله عنه) said: The Messenger of Allah (ﷺ) said: "In the case of buried treasure, the khumus must be paid.”
Musnad Ahmad 3276Saheeh, because of corroborating evidence]