Sahih Bukhari Volume 1, Book 3, Hadith 125

حَدَّثَنَا قَيْسُ بْنُ حَفْصٍ، قَالَ حَدَّثَنَا عَبْدُ الْوَاحِدِ، قَالَ حَدَّثَنَا الأَعْمَشُ، سُلَيْمَانُ عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ بَيْنَا أَنَا أَمْشِي، مَعَ النَّبِيِّ صلى الله عليه وسلم فِي خَرِبِ الْمَدِينَةِ، وَهُوَ يَتَوَكَّأُ عَلَى عَسِيبٍ مَعَهُ، فَمَرَّ بِنَفَرٍ مِنَ الْيَهُودِ، فَقَالَ بَعْضُهُمْ لِبَعْضٍ سَلُوهُ عَنِ الرُّوحِ‏.‏ وَقَالَ بَعْضُهُمْ لاَ تَسْأَلُوهُ لاَ يَجِيءُ فِيهِ بِشَىْءٍ تَكْرَهُونَهُ‏.‏ فَقَالَ بَعْضُهُمْ لَنَسْأَلَنَّهُ‏.‏ فَقَامَ رَجُلٌ مِنْهُمْ فَقَالَ يَا أَبَا الْقَاسِمِ، مَا الرُّوحُ فَسَكَتَ‏.‏ فَقُلْتُ إِنَّهُ يُوحَى إِلَيْهِ‏.‏ فَقُمْتُ، فَلَمَّا انْجَلَى عَنْهُ، قَالَ ‏{‏وَيَسْأَلُونَكَ عَنِ الرُّوحِ قُلِ الرُّوحُ مِنْ أَمْرِ رَبِّي وَمَا أُوتُيتُمْ مِنَ الْعِلْمِ إِلاَّ قَلِيلاً‏}‏‏.‏ قَالَ الأَعْمَشُ هَكَذَا فِي قِرَاءَتِنَا‏

Narrated By 'Abdullah : While I was going with the Prophet through the ruins of Medina and he was reclining on a date-palm leaf stalk, some Jews passed by. Some of them said to the others: Ask him (the Prophet) about the spirit. Some of them said that they should not ask him that question as he might give a reply which would displease them. But some of them insisted on asking, and so one of them stood up and asked, "O Aba-l-Qasim ! What is the spirit?" The Prophet remained quiet. I thought he was being inspired Divinely. So I stayed till that state of the Prophet (while being inspired) was over. The Prophet then said, "And they ask you (O Muhammad) concerning the spirit... Say: The spirit... its knowledge is with my Lord. And of knowledge you (mankind) have been given only a little)." (17.85)