Musnad Ahmad 32:1878

'Affan narrated to us, Yazid bin Zuray' narrated to us, Sa'id bin Abi 'Aruba narrated to us, from Hajjaj al-Ahwal, from Qatadah, from Anas, from the Prophet (peace and blessings of Allah be upon him), who said: "Whoever forgets a prayer, or sleeps through it—meaning—let him pray it." He said: So I met Hajjaj al-Ahwal and he narrated it to me.