Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: This verse was revealed: "Your wives are a tilth for you." It was revealed concerning some people from the Ansar who came to the Prophet (peace and blessings be upon him) and asked him, and the Prophet (peace and blessings be upon him) said: "You may go to her in any position, provided the intercourse is in the front passage."
Ahmad recorded it; its chain contains a narrator, Rishdin bin Sa'd, who is da'if (weak). (Allamah al-Haythami says:) I say: Some hadiths of this kind have already passed in the chapter on marriage.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 10864