It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that once Sayyiduna Umar Farooq (may Allah be pleased with him) came to the service of the Prophet (peace and blessings be upon him) and said: "O Messenger of Allah (peace and blessings be upon him)! I am ruined." The Prophet (peace and blessings be upon him) asked: "What has ruined you?" He replied: "Last night I turned my mount (approached my wife from behind in the front passage)." The Prophet (peace and blessings be upon him) did not give any answer to this. After a short while, Allah revealed this verse to His Prophet: «﴿نِسَاؤُكُمْ حَرْثٌ لَكُمْ فَأْتُوا حَرْثَكُمْ أَنَّى شِئْتُمْ﴾ [البقرة: 223] » "Your wives are your tilth, so come to your tilth as you wish." Whether from the front or from behind, but avoid the back passage and during menstruation.