In a narration from Sayyiduna Anas (may Allah be pleased with him) he reported these words: He narrated that the Prophet (peace and blessings be upon him) said: "The days were presented to me, and among them the day of Friday was presented to me. It was like a white mirror, in the middle of which there was a black spot. I asked: 'What is this (black spot)?' I was told: 'The Hour.'" The narrators of this narration are the narrators of the Sahih, except for the teacher of Imam al-Tabarani, and he is thiqah (trustworthy).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2997