Musannaf Ibn Abi Shayba 21:515

Abu Khalid narrated to us, from Ibn Hurmuz, from Mujahid, from Ibn Abbas, who said: "Upon the Yemeni Corner is an angel who says, 'Amen.' So when you pass by it, say: 'O Allah, our Lord, give us in this world [that which is] good and in the Hereafter [that which is] good and protect us from the punishment of the Fire.'"