What is the ruling concerning a group that withholds Zakat?

The group that withholds zakat (definition), if they deny its obligation out of ignorance, and they are excusable for such ignorance due to their recent conversion to Islam or their upbringing in a remote desert far from cities, they should be informed of its obligation, and they are not to be declared disbelievers. However, if a Muslim grew up in Islamic lands among scholars, and then denies it, he is considered an apostate who should be given three days to repent; otherwise, he is to be executed. If he withholds it while believing in its obligation, and the Imam is able to take it from him, he should take it and punish him. But if the one withholding zakat is outside the Imam's control, the Imam should fight him, based on the fighting of the Companions against those who withheld it, and the statement of Abu Bakr Al-Siddiq (may Allah be pleased with him): "If they withhold from me even a rope they used to pay to the Messenger of Allah (peace be upon him), I would fight them for it."