ENOfficial
Narrated Asma', daughter of Yazid ibn as-Sakan,: I heard the Messenger of Allah (ﷺ) as saying: Do not kill your children secretly, for the milk, with which a child is suckled while his mother is pregnant, overtakes the horseman and throws him from his horse.
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا الرَّبِيعُ بْنُ نَافِعٍ أَبُو تَوْبَةَ، حَدَّثَنَا مُحَمَّدُ بْنُ مُهَاجِرٍ، عَنْ أَبِيهِ، عَنْ أَسْمَاءَ بِنْتِ يَزِيدَ بْنِ السَّكَنِ، قَالَتْ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " لاَ تَقْتُلُوا أَوْلاَدَكُمْ سِرًّا فَإِنَّ الْغَيْلَ يُدْرِكُ الْفَارِسَ فَيُدَعْثِرُهُ عَنْ فَرَسِهِ " .
sunnah.com