Subul us Salaam (Paths to Peace)

Origin of al-Khawārij
The first and worst of the Kharijites was Dhu'l-Khuwaysirah.
Abu Sa'id Al-Khudri (may Allah be Pleased with him) said: 'Ali Ibn Abi Talib (may Allah be Pleased with him) sent a piece of gold not yet taken out of its ore, in a tanned leather container to Allah's Messenger (Peace be upon him) who distributed that...

Abu Ayyub Ansāri (may Allah be pleased with him) narrated that the Messenger of Allah (Peace be upon Him) said:
Whoever fasts Ramadān then follows it with six days of [fasting in] in Shawwāl, it is as if he fasted a lifetime. [Sahih Muslim (1164)]
According to this formula there is a minimum ten-fold reward for every virtue, the saūm of one month of (Ramadān) is equivalent to the saūm of ten months. If one also observe the six days of saūm of Shawwāl, they will equal to saūm of two months. Thus...

1. Being Muslim
Fasting is not accepted from a disbeliever because the fast is one of the pillars of Islam. Allah's Messenger (Peace be upon him) said:
Islam is based on (the following) five (Principles):

Allah says:
And eat and drink but waste not by extravagance, certainly He (Allah) likes not Al-Musrifun (those who was to by extravagance). [Qur'an (7):31]
Abu Hurairah (may Allah be pleased with him) narrated that Messenger of Allah (Peace be upon him) hosted a guest who was a disbeliever. The Messenger of Allah (Peace be upon him) ordered that a sheep be milked for him and he drank it, then another and...