Musnad Abu Ya'la al-Mawsili 42:423

And from Abu Sa'id al-Khudri, from the Messenger of Allah, may Allah bless him and grant him peace, that he said: "And raised couches" (al-Waqi'ah: 34). He said: "By the One in Whose hand is my soul, indeed their height is like what is between the heaven and the earth. And indeed, what is between the heaven and the earth is a journey of five hundred years."