Urwah narrates from Sayyidah Aishah (may Allah be pleased with her): My foster uncle Aflah asked permission to come in to me, and I veiled myself from him. Then I told the Prophet (peace and blessings be upon him), and the Messenger of Allah (peace and blessings be upon him) said: "Do not veil yourself from him, for the relations that are unlawful through lineage become unlawful through suckling as well." Muslim narrated it in the Sahih from Qutaybah.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرضاع / 15611