Breastfeeding is because of Hunger (meaning, during infancy)
حَدَّثَنَا هَنَّادُ بْنُ السَّرِيِّ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ أَشْعَثَ بْنِ أَبِي الشَّعْثَاءِ، عَنْ أَبِيهِ، عَنْ مَسْرُوقٍ، قَالَ قَالَتْ عَائِشَةُ دَخَلَ عَلَىَّ رَسُولُ اللَّهِ صلى الله عليه وسلم وَعِنْدِي رَجُلٌ قَاعِدٌ فَاشْتَدَّ ذَلِكَ عَلَيْهِ وَرَأَيْتُ الْغَضَبَ فِي وَجْهِهِ قَالَتْ فَقُلْتُ يَا رَسُولَ اللَّهِ إِنَّهُ أَخِي مِنَ الرَّضَاعَةِ . قَالَتْ فَقَالَ " انْظُرْنَ إِخْوَتَكُنَّ مِنَ الرَّضَاعَةِ فَإِنَّمَا الرَّضَاعَةُ مِنَ الْمَجَاعَةِ".
'A'isha (Allah be pleased with her) reported: Allah's Messenger (ﷺ) visited me when a man was sitting near me, and he seemed to disapprove of that. And I saw signs of anger on his face and I said: Messenger of Allah, he is my brother by forsterage, whereupon he said: Consider who your brothers are because of fosterage since fosterage is through hunger (i. e. in infancy).