مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2686
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: 'Umar bin al-Khattab came to the Messenger of Allah (ﷺ) and said: O Messenger of Allah, I am doomed! He said: "What has doomed you?” He said: I had intercourse from behind yesterday. He did not reply, then Allah revealed this verse to His Messenger: “Your wives are a tilth for you, so go to your tilth, when or how you will" (al-Baqarah 2:223). (The Prophet (ﷺ)) said: “From the front or from behind, but avoid the back passage and the time of menstruation."
Musnad Ahmad 2703. [Its isnad is hasan]