Narrated Ibn Mas'ud:

While I was walking in company with the Prophet in one of the fields of Medina, the Prophet was reclining on a palm leave stalk which he carried with him. We passed by a group of Jews. Some of them said to the others, "Ask him about the spirit." The others said, "Do not ask him, lest he would say something that you hate." Some of them said, "We will ask him." So a man from among them stood up and said, 'O Abal-Qasim! What is the spirit?" The Prophet kept quiet and I knew that he was being divinely inspired. Then he said: "They ask you 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)

حَدَّثَنَا مُوسَى بْنُ إِسْمَاعِيلَ، عَنْ عَبْدِ الْوَاحِدِ، عَنِ الأَعْمَشِ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنِ ابْنِ مَسْعُودٍ، قَالَ بَيْنَا أَنَا أَمْشِي، مَعَ النَّبِيِّ ﷺ فِي بَعْضِ حَرْثِ الْمَدِينَةِ وَهْوَ يَتَوَكَّأُ عَلَى عَسِيبٍ مَعَهُ، فَمَرَرْنَا عَلَى نَفَرٍ مِنَ الْيَهُودِ فَقَالَ بَعْضُهُمْ لِبَعْضٍ سَلُوهُ عَنِ الرُّوحِ. فَقَالَ بَعْضُهُمْ لاَ تَسْأَلُوهُ أَنْ يَجِيءَ فِيهِ بِشَىْءٍ تَكْرَهُونَهُ. فَقَالَ بَعْضُهُمْ لَنَسْأَلَنَّهُ. فَقَامَ إِلَيْهِ رَجُلٌ مِنْهُمْ فَقَالَ يَا أَبَا الْقَاسِمِ مَا الرُّوحُ فَسَكَتَ عَنْهُ النَّبِيُّ ﷺ فَعَلِمْتُ أَنَّهُ يُوحَى إِلَيْهِ فَقَالَ {وَيَسْأَلُونَكَ عَنِ الرُّوحِ قُلِ الرُّوحُ مِنْ أَمْرِ رَبِّي وَمَا أُوتُوا مِنَ الْعِلْمِ إِلاَّ قَلِيلاً}. قَالَ الأَعْمَشُ هَكَذَا فِي قِرِاءَتِنَا.