Sayyiduna Uqbah bin Amir al-Juhani (may Allah be pleased with him) said: During a military expedition, I was leading the mount of the Messenger of Allah (peace and blessings be upon him) when he (peace and blessings be upon him) said: "Say, O Uqbah." I said: What shall I say? He said it a third time, and I again said: What shall I say? He (peace and blessings be upon him) said: Recite 'Qul huwa Allahu ahad'. Then he (peace and blessings be upon him) recited the whole surah until he completed it. Then he recited Surah al-Falaq, and I recited it with him until we completed it. Then he recited Surah al-Nas, and I recited it with him until we completed it. Then he (peace and blessings be upon him) said: "Refuge has never been sought with anything like them."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 15023