Riyad U Saliheen, Hadith # 208
Mu`adh
 (May Allah be pleased with him) reported that Messenger of Allah (PBUH)
 sent me (as a governor of Yemen) and instructed me thus: "You will go 
to the people of the Book. First call them to testify that `there is no 
true god except Allah, that I am (Muhammad (PBUH)) the Messenger of 
Allah.' If they obey you, tell them that Allah has enjoined upon them 
five Salat (prayers) during the day and night; and if they obey you, 
inform them that Allah has made Zakat obligatory upon them; that it 
should be collected from their rich and distributed among their poor; 
and if they obey you refrain from picking up (as a share of Zakat) the 
best of their wealth. Beware of the supplication of the oppressed, for 
there is no barrier  between it and Allah".
[Al-Bukhari and Muslim].
Commentary:
1.
 If it comes to Jihad against infidels, polytheists and the people of 
the Book (Ahl-ul-Kitab) then before waging war against them, they should
 be invited to Islam and told about the prescribed Salat (prayers), 
Zakat and other teachings of Islam.
2. The Zakat collected from 
the rich of a locality must be spent on the poor of that place. If some 
amount is left unspent only then it should be distributed among the 
deserving people of other areas.
3. The collectors of Zakat 
should refrain from aggression in its collection as in that case they 
will be invoking the curse of the people concerned and thereby invite 
the Wrath of Allah.