Is there a Hadith that declares taking a fatwa without evidence to be an act of disbelief or unlawful, and where can it be found if it exists?

We are not aware of any Hadith that obligates declaring a questioner an infidel or embarrassing them if they seek a fatwa from a trustworthy, knowledgeable mufti who does not mention the evidence. The Companions and their successors (Tabi'un) used to issue fatwas, and people would accept them without the evidence being mentioned. However, the questioner must take their religion from someone whose knowledge, trustworthiness, and adherence to evidence are reliable, and they are permitted to ask the mufti for the evidence. As for taking a fatwa from an ignorant person who issues rulings without knowledge, it is forbidden and a cause for misguidance and fabrication against Allah. The prohibition has been mentioned in His (the Almighty's) saying: "Say, 'My Lord has only forbidden immoralities – what is apparent of them and what is concealed – and sin, and oppression without right, and that you associate with Allah that for which He has not sent down authority, and that you say about Allah what you do not know.'" (7:33), and His saying: "And do not say about what your tongues falsely describe, 'This is lawful and this is unlawful,' to invent falsehood about Allah. Indeed, those who invent falsehood about Allah will not succeed. A brief enjoyment, and for them is a painful punishment." (16:116-117). And the Prophet, peace and blessings be upon him, said: "Indeed, Allah does not seize knowledge by snatching it from people, but rather by taking away the scholars, until when no scholar remains, people will appoint ignorant leaders. They will be asked, and they will issue fatwas without knowledge, so they will go astray and lead others astray."