What actions invalidate the spiritual reward of fasting?

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The fasting person must purify their fast from lying, backbiting, and insulting. Ahmad stated that the fasting person ought to guard their tongue, avoid wrangling, and preserve their fast. The Prophet Muhammad, peace be upon him, stated: 'Whoever does not give up false speech and acting upon it, Allah has no need of his leaving his food and drink.' Furthermore, Allah states concerning the fast: 'Every deed of the son of Adam is for him, except for the fast, as it is for Me, and I reward for it.' The fast acts as a shield. If someone insults or fights the fasting person, the person should declare, 'I am a person who is fasting.' The breath of the fasting person is more beloved to Allah than the scent of musk.