I intended to prohibit cohabitation with a suckling woman until I considered that the Romans and the Persians do it without any injury being caused to their children thereby. (Imam Muslim said: Khalaf reported it from Judamat al-'Asadiyya, but the correct wording is what has been stated by Yahya.)  

أَنَّهَا سَمِعَتْ رَسُولَ اللَّهِ ﷺ يَقُولُ لَقَدْ هَمَمْتُ أَنْ أَنْهَى عَنِ الْغِيلَةِ حَتَّى ذَكَرْتُ أَنَّ الرُّومَ وَفَارِسَ يَصْنَعُونَ ذَلِكَ فَلاَ يَضُرُّ أَوْلاَدَهُمْ قَالَ مُسْلِمٌ وَأَمَّا خَلَفٌ فَقَالَ عَنْ جُذَامَةَ الأَسَدِيَّةِ وَالصَّحِيحُ مَا قَالَهُ يَحْيَى بِالدَّالِ  

I went to Messenger of Allah ﷺ along with some persons and he was saying: I intended to prohibit cohabitation with the suckling women, but I considered the Greeks and Persians, and saw that they suckle their children and this thing (cohabitation) does not do any harm to them (to the suckling women). Then they asked him about 'azl, whereupon he said. That is the secret (way of) burying alive, and Ubaidullah has made this addition in the hadith transmitted by al-Muqri and that is:" When the one buried alive is asked."  

حَضَرْتُ رَسُولَ اللَّهِ ﷺ فِي أُنَاسٍ وَهُوَ يَقُولُ لَقَدْ هَمَمْتُ أَنْ أَنْهَى عَنِ الْغِيلَةِ فَنَظَرْتُ فِي الرُّومِ وَفَارِسَ فَإِذَا هُمْ يُغِيلُونَ أَوْلاَدَهُمْ فَلاَ يَضُرُّ أَوْلاَدَهُمْ ذَلِكَ شَيْئًا ثُمَّ سَأَلُوهُ عَنِ الْعَزْلِ فَقَالَ رَسُولُ اللَّهِ ﷺ ذَلِكَ الْوَأْدُ الْخَفِيُّ زَادَ عُبَيْدُ اللَّهِ فِي حَدِيثِهِ عَنِ الْمُقْرِئِ وَهْىَ { وَإِذَا الْمَوْءُودَةُ سُئِلَتْ}  

I heard Messenger of Allah ﷺ saying this. The rest of the hadith is the same concerning 'azl and ghila (cohabitating with a suckling woman), but with a slight variation of words.  

أَنَّهَا قَالَتْ سَمِعْتُ رَسُولَ اللَّهِ ﷺ فَذَكَرَ بِمِثْلِ حَدِيثِ سَعِيدِ بْنِ أَبِي أَيُّوبَ فِي الْعَزْلِ وَالْغِيلَةِ غَيْرَ أَنَّهُ قَالَ الْغِيَالِ  

I do 'azi with my wife. Thereupon Messenger of Allah ﷺ said: Why do you do that? The person said: I fear harm to her child or her children. Thereupon Messenger of Allah (way peace be upon him) said: If that were harmful it would harm the Persians and the Greeks.  

أَنَّ رَجُلاً جَاءَ إِلَى رَسُولِ اللَّهِ ﷺ فَقَالَ إِنِّي أَعْزِلُ عَنِ امْرَأَتِي فَقَالَ لَهُ رَسُولُ اللَّهِ ﷺ لِمَ تَفْعَلُ ذَلِكَ فَقَالَ الرَّجُلُ أُشْفِقُ عَلَى وَلَدِهَا أَوْ عَلَى أَوْلاَدِهَا فَقَالَ رَسُولُ اللَّهِ ﷺ لَوْ كَانَ ذَلِكَ ضَارًّا ضَرَّ فَارِسَ وَالرُّومَ وَقَالَ زُهَيْرٌ فِي رِوَايَتِهِ إِنْ كَانَ لِذَلِكَ فَلاَ مَا ضَارَ ذَلِكَ فَارِسَ وَلاَ الرُّومَ