Mishkat al-Masabih 3162
She said:
My paternal uncle through fosterage came and asked permission to enter, but I refused to allow him till I asked God’s Messenger. When he came I asked him and he said, “He is your paternal uncle, so give him permission.” I replied, “Messenger of God, it was only the woman who suckled me and not the man” whereupon he said, “He is your paternal uncle, so let him come in where you are.” That was after seclusion was instituted for us. 

(Bukhari and Muslim.)
وَعَنْهَا قَالَتْ: جَاءَ عَمِّي مِنَ الرَّضَاعَةِ فَاسْتَأْذَنَ عَلَيَّ فَأَبَيْتُ أَنْ آذَنَ لَهُ حَتَّى أَسْأَلَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَجَاءَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ فَسَأَلْتُهُ فَقَالَ: «أَنَّهُ عَمُّكِ فَأْذَنِي لَهُ» قَالَت: فَقلت: يَا رَسُولَ اللَّهِ إِنَّمَا أَرْضَعَتْنِي الْمَرْأَةُ وَلَمْ يرضعني الرَّجُلُ فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «إِنَّه عمك فليلج عَلَيْك» وَذَلِكَ بَعْدَمَا ضرب علينا الْحجاب