It is narrated on the authority of Abu Umama that the Messenger ﷺ observed: He who appropriated the right of a Muslim by (swearing a false) oath, Allah would make Hell-fire necessary for him and declare Paradise forbidden for him. A person said to him: Messenger of Allah, even if it is something insignificant? He (the Blessed Messenger) replied: (Yes) even if it is the twig of the arak tree.
(Sahih Muslim)
For a Muslim nothing is so damaging as the fact that he should go to the extent of taking a false oath in the name of Allah and that too for some material benefit over which he has no legitimate claim. It implies that such a person has no fellow feeling, no respect for the Lord, and he is absolutely bereft of the sense of fairness and justice and devoured by a lust for material possession.
Imam Nawawi has made it clear that it is wrong to infer on the basis of this hadith that high-handedness is permissible in case of a non-Muslim. The right of a non-Muslim must also be respected, for Islam does not permit its infringement. Here in this hadith the word ‘Muslim’ has been stressed with a view to emphasising the fact that apart from other considerations, the person has no regard even for the brotherhood of faith.
Arak is a kind of tree well-known in Arabia and bears what resembles the bunches of grapes and of which the sticks of cleaning the teeth are made and camels feed on its leaves.