Hadithcore
Hadith #2114310

Ahmad reported it from the Hadith of 'Ali (RA), he said, "The little girl must be with her maternal aunt for the maternal aunt is (the same as) a mother."

وَأَخْرَجَهُ أَحْمَدُ: مِنْ حَدِيثِ عَلَيٍّ فَقَالَ: { وَالْجَارِيَةُ عِنْدَ خَالَتِهَا, فَإِنَّ اَلْخَالَةَ وَالِدَةٌ } [1]‏

References2 variants
Sunnah.com reference
Book 8, Hadith 220
Arabic/English book reference
Book 8, Hadith 1166