Musnad Abu Ya'la al-Mawsili 152:322

Abu Khaythama narrated to us, Waki' narrated to us, al-A'mash narrated to us, from Ibrahim, from 'Alqama, from 'Abdullah, who said: I was with the Prophet, may Allah bless him and grant him peace, in a cultivated field in Medina, and he was leaning upon a palm branch of his. He passed by a group of the Jews, and some of them said, "Do not ask him." But they asked him. He leaned upon the palm branch as if he were receiving revelation. Then he said: "And they ask you about the soul. Say, 'The soul is of the affair of my Lord. And you have not been given of knowledge except a little.'"