Musnad Ahmad 1013:23

Ahmad ibn Abd al-Malik narrated to us, Hammad ibn Zayd narrated to us, from Abu Hazim, from Sahl ibn Sa’d, from the Prophet, peace and blessings of Allah be upon him, who said: "Indeed, for Paradise there is a gate called al-Rayyan. It is said: On the Day of Resurrection, 'Where are the fasting ones?' Come forth to al-Rayyan. So when the last of them enters, that gate is closed."