Musnad Ahmad 1012:73

'Abd al-Samad narrated to us, Hammam narrated to us, Zayd ibn Aslam narrated to us, from 'Ata' ibn Yasar, from 'Ubadah ibn al-Samit, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Paradise has one hundred degrees. Between every two degrees of them is like what is between the heaven and the earth. Al-Firdaws is the highest of them in degree, and from it gush forth the four rivers of Paradise, and above it is the Throne. So when you ask Allah, ask Him for Al-Firdaws."