Sayyiduna Abu Qabil (may Allah be pleased with him) narrates: We came to Sayyiduna Abdullah bin Amr (may Allah be pleased with him), and he was asked: "Which city will be conquered first, Constantinople or Rome?" The narrator says: Sayyiduna Abdullah (may Allah be pleased with him) sent for his chest and took out a document from it. Sayyiduna Abdullah (may Allah be pleased with him) said: Once we were sitting around the Prophet (peace and blessings be upon him), writing, when the Prophet (peace and blessings be upon him) was asked: "Which of the two cities will be conquered (first), Constantinople or Rome?" The Prophet (peace and blessings be upon him) said: "The city of Heraclius will be conquered first." The narrator says: This means Constantinople.
Ahmad recorded it, and its narrators are the narrators of the Sahih, except the narrator Abu Qabil, and he is thiqah (trustworthy).