Sahih Muslim 2794 a
`Abdullah (b. Mas`ud) reported:
As I was going along with Allah's Apostle (ﷺ) in a cultivable land and he (the Holy Prophet) was walking with the support of a wood, a group of Jews happened to meet him. Some of them said to the others: Ask him about the Soul. They said: What is your doubt about it? There is a possibility that you may ask him about anything (the answer of) which you may not like. They said: Ask him. So one amongst them asked him about the Soul. Allah's Messenger (ﷺ) kept quiet and he gave no reply and I came to know that revelation was being sent to him, so I stood at my place and thus this revelation descended upon him:" They ask thee about the Soul. Say: The Soul is by the Commandment of my Lord, and of Knowledge you are given but a little" (xvii. 58).
حَدَّثَنَا عُمَرُ بْنُ حَفْصِ بْنِ غِيَاثٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا الأَعْمَشُ، حَدَّثَنِي إِبْرَاهِيمُ،
 عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ بَيْنَمَا أَنَا أَمْشِي، مَعَ النَّبِيِّ صلى الله عليه وسلم فِي حَرْثٍ
 وَهُوَ مُتَّكِئٌ عَلَى عَسِيبٍ إِذْ مَرَّ بِنَفَرٍ مِنَ الْيَهُودِ فَقَالَ بَعْضُهُمْ لِبَعْضٍ سَلُوهُ عَنِ الرُّوحِ فَقَالُوا
 مَا رَابَكُمْ إِلَيْهِ لاَ يَسْتَقْبِلُكُمْ بِشَىْءٍ تَكْرَهُونَهُ ‏.‏ فَقَالُوا سَلُوهُ فَقَامَ إِلَيْهِ بَعْضُهُمْ فَسَأَلَهُ عَنِ
 الرُّوحِ - قَالَ - فَأَسْكَتَ النَّبِيُّ صلى الله عليه وسلم فَلَمْ يَرُدَّ عَلَيْهِ شَيْئًا فَعَلِمْتُ أَنَّهُ يُوحَى
 إِلَيْهِ - قَالَ - فَقُمْتُ مَكَانِي فَلَمَّا نَزَلَ الْوَحْىُ قَالَ ‏{‏ وَيَسْأَلُونَكَ عَنِ الرُّوحِ قُلِ الرُّوحُ مِنْ
 أَمْرِ رَبِّي وَمَا أُوتِيتُمْ مِنَ الْعِلْمِ إِلاَّ قَلِيلاً‏}‏