Mishkat al-Masabih 29 Excellent Qualities and Description of the Prophet كتاب الفضائل والشمائل 112

وَعَن أنسٍ قَالَ: إِنَّ أَهْلَ مَكَّةَ سَأَلُوا رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَنْ يُرِيَهُمْ آيَةً فَأَرَاهُمُ الْقَمَرَ شِقَّتَيْنِ حَتَّى رَأَوْا حِرَاءً بَيْنَهُمَا. مُتَّفق عَلَيْهِ

Anas said that when the people of Mecca asked God’s messenger to show them a sign, he showed them the moon in two pieces between which they were able to see Hira. (Bukhari and Muslim.)