It is narrated from Hazrat Aisha (may Allah be pleased with her) that the Prophet (peace and blessings be upon him) said: The relationships that become unlawful due to lineage also become unlawful due to breastfeeding.
Hadith Referenceمسند احمد / مسند النساء / 24431
Hadith Gradingحکم دارالسلام:حديث صحيح، وهذا إسناد ضعيف لضعف شريك