Sayyiduna al-Harith bin Malik bin Barsa' (may Allah be pleased with him) said: I heard the Prophet (peace and blessings be upon him) say on the day of the Conquest of Makkah: "After today, it will never be attacked again until the Day of Resurrection."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3322