If you're clever, you can use it 8 times in a sentence:Another matter raised - is there any rule to repeating a word in a sentence? I know there’s an argument to suggest it’s a big no no, but it really depends on the context. Sometimes the repetition of a word is to put extra emphasis on it. I don’t know if there’s really any rule to say they can’t repeat ‘believe’ three times in a sentence? What might well regarded English playwright Jez Butterworth say in his defence?
I don't think there's a "rule," per se, but it's just generally frowned upon. I do a lot of proofreading and copy-editing at work (not that you could tell by the number of typos and errors I make in my posts on this site), and I usually try to reword things when I see repetition within a sentence or even within two adjacent sentences.
Creative Writer by trade, clever comedian by reputation.