Musnad Abu Ya'la al-Mawsili 3:282

Abu Musa narrated to us, Mansur bin Wardan al-Asadi narrated to us, Ali bin Abd al-A’la narrated to us, from his father, from Abu al-Bakhtari, from Ali, who said: When this verse was revealed: "And [due] to Allah from the people is a pilgrimage to the House - for whoever is able to find thereto a way" [Al-Imran: 97], they said: "O Messenger of Allah, is it every year?" He remained silent. Then they said: "Is it every year?" He said: "No, and if I had said yes, it would have become obligatory." Then Allah revealed: "O you who have believed, do not ask about things which, if they are shown to you, will distress you" [Al-Ma'idah: 101], until the end of the verse.