How to get answers *only* from the given documents?

[KonradHoeffner]

localGPT works great for questions that are answered only in the given documents.
But when something has a different meaning in the specific domain of the given documents, I often get wrong answers based on what the model already knows.
How can I make sure that answers are only based on the given documents?

For example, if my document says that the sky is yellow, how do I prevent the model from saying that the sky is blue?
I already modified the template as follows but this didn't work:

template = """Use the following pieces of context to answer the question at the end. If you don't know the answer,\
    just say that you don't know, don't try to make up an answer. Answer the question only using the given context.
    Say explicitly if the question cannot be answered using the given text but only with your existing knowledge.
    Also state explicitly if there is a conflict between what you know already and what is stated in the given text.

    {context}

    {history}
    Question: {question}
    Helpful Answer:"""