الحديث 3056
وَعنهُ كُنَّا نَعْزِلُ وَالْقُرْآنُ يَنْزِلُ. مُتَّفَقٌ عَلَيْهِ. وَزَادَ مُسْلِمٌ: فَبَلَغَ ذَلِكَ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَلم ينهنا
ترجمة sunnah.com، ليست من لفظ الكتاب
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.