“Avoid those that are lactating.” (i.e. those from which milk is received).  

أَنَّ رَسُولَ اللَّهِ ﷺ أَتَى رَجُلاً مِنَ الأَنْصَارِ فَأَخَذَ الشَّفْرَةَ لِيَذْبَحَ لِرَسُولِ اللَّهِ ﷺ فَقَالَ لَهُ رَسُولُ اللَّهِ ﷺ إِيَّاكَ وَالْحَلُوبَ  

“Let us go out to Waqifi.” He said: “So we went out in the moonlight until we came to the garden and he (the owner of the garden) said: ‘Welcome.’ Then he took up the knife and went among the sheep (to choose one for slaughter), and the Messenger of Allah ﷺ said: ‘Avoid those that are lactating.’”  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لَهُ وَلِعُمَرَ انْطَلِقُوا بِنَا إِلَى الْوَاقِفِيِّ قَالَ فَانْطَلَقْنَا فِي الْقَمَرِ حَتَّى أَتَيْنَا الْحَائِطَ فَقَالَ مَرْحَبًا وَأَهْلاً ثُمَّ أَخَذَ الشَّفْرَةَ ثُمَّ جَالَ فِي الْغَنَمِ فَقَالَ رَسُولُ اللَّهِ ﷺ إِيَّاكَ وَالْحَلُوبَ أَوْ قَالَ ذَاتَ الدَّرِّ