Mishkat al-Masabih 13 Marriage كتاب النكاح 102

وَعنهُ كُنَّا نَعْزِلُ وَالْقُرْآنُ يَنْزِلُ. مُتَّفَقٌ عَلَيْهِ. وَزَادَ مُسْلِمٌ: فَبَلَغَ ذَلِكَ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَلم ينهنا

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.