Abu Sa'id al-Khudri (Allah be pleased with him) reported that Allah's Apostle (ﷺ) was asked about 'azl, whereupon he said
There is no harm if you do not do that, for it (the birth of the child) is something ordained. Muhammad (one of the narrators) said: (The words) La 'alaykum (there is no harm) implies its Prohibition.