Explanation

‘Uqbah ibn ‘Āmir (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Have you not seen," i.e. "Don't you know?" Though he is addressing ‘Uqbah in particular, the purpose is to address everyone in general. This is a rhetorical question to express wonder, and he referred to the reason for such wonder in his statement: "the like of which has never been seen before," i.e. they are unprecedented in their category which is "Isti‘ādhah", or seeking refuge in Allah. He said "never" to emphasize that they are unprecedented. His statement: "They are: {Say: I seek refuge with the Lord of the daybreak} [Sūrat al-Falaq], and {Say: I seek refuge with the Lord of mankind} [Sūrat An-Nās]," i.e. there are no verses of a Qur'anic Sūrah which all serve to give refuge to their reciter from the evil of all evils like the verses of these two Sūrahs. Anyone who seeks refuge with these verses while having sincere faith, Allah, the Almighty will grant him refuge. In brief, the Muslim should seek refuge from evil by reciting these two Sūrahs.