Musnad Abu Ya'la al-Mawsili 153:140

Al-Fadl ibn al-Sabah narrated to me, Ma'n ibn 'Isa narrated to me, Khalid ibn Abi Bakr ibn 'Ubayd Allah ibn 'Umar narrated to us, from Salim ibn 'Abd Allah, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The gate of my Ummah through which they will enter Paradise has a width equal to the journey of a swift rider—a swift rider, a swift rider—for three [days]. They will be crowding upon it to the extent that their shoulders will almost be dislocated."