مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3887
Musnad of Abdullah bin Mas'ood
It was narrated from Ibn Mas'ood (رضي الله عنه) from The Prophet (ﷺ) that he said: "The eyes commit zina, the hands commit zina, the feet commit zina, and the private part commits zina.”
Musnad Ahmad 3912A saheeh hadeeth; this is a hasan isnad]