عَنْ جَابِرٍ قَالَ: كَانَتِ الْيَهُودُ تَقُولُ: إِذَا أَتَى الرَّجُلُ امْرَأَتَهُ مِنْ دُبُرِهَا فِي قُبُلِهَا كَانَ الْوَلَد أَحول فَنزلت: (نساوكم حرث لكم فَأتوا حَرْثكُمْ أَنى شِئْتُم)

He said that in the period when the Qur'an was coming down they used to withdraw the penis.* * i.e. before emission of semen, to avoid conception.(Bukhari and Muslim.) Muslim added that the Prophet heard of that and did not prohibit it.