It is narrated from Khalid bin Abi Jabal al-Adwani (may Allah be pleased with him) that he saw the Messenger of Allah (peace and blessings be upon him) in the eastern part of Thaqif, standing leaning on a bow or a staff, at the time when he had come to them seeking their support. He said: I heard him recite 'Wa al-sama'i wa al-tariq' (By the sky and the night-comer) until he completed it. He said: I memorised it in the time of Ignorance (Jahiliyyah) while I was a polytheist, then I recited it (again) in Islam. The people asked: "What did you hear from this man?" So I recited that surah to them. At this, the people of Quraysh who were with them said: "We know our man better; had we known that what he says is the truth, we would have followed him."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4112