Mujahid (may Allah have mercy on him) said: I read the Qur'an to Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) twice, and I asked him about this verse: "Your wives are a tilth for you, so come to your tilth however you wish." [Surah al-Baqarah: 223] He said: Come to her from the place that was made forbidden; come from where menstruation and childbirth take place.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 14108