Musannaf Ibn Abi Shayba 33:1000

Al-Husayn ibn Ali narrated to us, from Abu Musa, from al-Hasan, who said: The Messenger of Allah (may Allah bless him and grant him peace) said to his companions: "You among the people are like salt in food." Then al-Hasan says: "And is food made good except with salt?" Then al-Hasan says: "So how will it be for a people whose salt has gone?"