مُسْنَدُ أَحْمَدَ
Musnad Ahmad 2402
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It was narrated that Ibn 'Abbas (رضي الله عنه) said: This verse - "Your wives are a tilth for you" [al-Baqarah 2:223] - it was revealed concerning some of the Ansar who came to the Prophet (ﷺ) and asked him, and the Messenger of Allah (ﷺ) said: "Have intercourse with her in any position, so long as it is in the vagina.”
Musnad Ahmad 2414Hasan, this is a da'eef isnad because of the weakness of Ris