Sayyiduna Ka'b bin Malik (may Allah be pleased with him) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "When Egypt is conquered, enjoin good treatment of the Copts, for they have a right of protection (dhimmah) and ties of kinship." That is, the mother of Sayyiduna Isma'il (peace be upon him) was from among them.
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16161