Sahih Bukhari Volume 6, Book 65, Hadith 4528

حَدَّثَنِى إِسْحَاقُ، أَخْبَرَنَا النَّضْرُ بْنُ شُمَيْلٍ، أَخْبَرَنَا ابْنُ عَوْنٍ، عَنْ نَافِعٍ، قَالَ كَانَ ابْنُ عُمَرَ ـ رضى الله عنهما ـ إِذَا قَرَأَ الْقُرْآنَ لَمْ يَتَكَلَّمْ حَتَّى يَفْرُغَ مِنْهُ، فَأَخَذْتُ عَلَيْهِ يَوْمًا، فَقَرَأَ سُورَةَ الْبَقَرَةِ حَتَّى انْتَهَى إِلَى مَكَانٍ قَالَ تَدْرِي فِيمَا أُنْزِلَتْ‏.‏ قُلْتُ لاَ‏.‏ قَالَ أُنْزِلَتْ فِي كَذَا وَكَذَا‏.‏ ثُمَّ مَضَى‏

Narrated By Nafi' : Whenever Ibn 'Umar recited the Qur'an, he would not speak to anyone till he had finished his recitation. Once I held the Qur'an and he recited Surat-al-Baqara from his memory and then stopped at a certain Verse and said, "Do you know in what connection this Verse was revealed? " I replied, "No." He said, "It was revealed in such-and-such connection."