Jami` at-Tirmidhi 3141

Narrated 'Abdullah:"I took a walk with the Prophet (ﷺ) on a farm in Al-Madinah, and when he reclined upon a palm-leaf stalk, a group of Jews were passing by. Some of them said, 'We should question him.' Others said: 'Do not question him for he might tell you something that you do not like.' They said to him: 'O Abul-Qasim, narrated to us about the Ruh.' The Prophet (ﷺ) stood for some time, he raised his head toward the heavens, and I recognized revelation was coming to him, until the revelation ceased. Then he (ﷺ) said: "The Ruh is one of the things, the knowledge of which is only with my Lord. And of knowledge, you have been given only a little (17:)