Is "Although he was tired, but he continued working" correct?

Why

Zoya's instinct that using more contrast words should make a contrast feel stronger is a reasonable guess about emphasis, similar to Vishal's "more better" mistake with comparisons. "Although" and "but" are both already doing the SAME single job here — signalling a contrast between being tired and continuing to work — so using both is a repetition, not an addition. "Although" already sets up the whole sentence to expect a contrast, which means the second half doesn't need its own separate contrast word; the contrast has already been announced. Using both together is exactly like Vishal's "more better": marking the same single idea twice when once is both correct and sufficient. Test: read the sentence with just one word each way — "Although he was tired, he continued working" and "He was tired, but he continued working" — both read as complete, correct sentences on their own, confirming that only one of the two words was ever needed. Her brother is right: "although" and "but" cannot be used together for the same contrast — choose one, either "although he was tired, he continued" or "he was tired, but he continued".