Surah At-Tawbah (Arabic: سورة التوبة, Sūratu at-Tawbah, "The Repentance") also known as al-Bara'ah "the Ultimatum" in many hadith is the ninth chapter of the Qur'an, with 129 verses (see, however, the discussion of ahadith 785-787 in Sunan Abi Dawood, relating to merging Suras 8 and 9, and the discussion of numbering the Basmala (q.v.)). It is one of the last Madinan Suras. It is the only Sura of the Qur'an that does not begin with the bismillah. The starting verses of this sura were revealed at the time of war. It is therefore that Allah demands the Muslims to fight under these situations.

It begins:
“ A (declaration) of immunity from Allah and His Messenger, to those of the Pagans with whom ye have contracted mutual alliances: Go ye, then, for four months, backwards and forwards, (as ye will), throughout the land, but know ye that ye cannot frustrate Allah (by your falsehood) but that Allah will cover with shame those who reject Him. ([Qur'an 9:1]) ”

The context of the sura is the Battle of Tabuk.

[Qur'an 9:5] The famous Sword verse reads as follows:
“ But when the forbidden months are past, then fight and slay the Pagans wherever ye find them, and seize them, beleaguer them, and lie in wait for them in every stratagem (of war); but if they repent, and establish regular prayers and practise regular charity, then open the way for them: for Allah is Oft-forgiving, Most Merciful. ”

At-Tawba 29 ([Qur'an 9:29]) reads as follows:
“ Fight against those who believe not in Allah nor the Last Day, nor hold that forbidden which hath been forbidden by Allah and His Messenger, nor acknowledge the religion of Truth, (even if they are) of the People of the Book, until they pay the Jizya with willing submission, and feel themselves subdued. ”

Verse 6: Istijarah

The Surah treats the relation of Muslims with non-Muslims, pagans, and also "People of the Book:
“ The Jews call 'Uzair the son of Allah, and the Christians call Christ the son of Allah. That is a saying from their mouth; (in this) they but imitate what the unbelievers of old used to say. Allah's curse be on them: how they are deluded away from the Truth! ([Qur'an 9:30]) ”

Verse [Qur'an 9:40] is about Hadith of Abu Bakr and Muhammad in the cave

Ayah 37 documents the Islamic prohibition of intercalation:

Verily the transposing (of a prohibited month) is an addition to Unbelief: The Unbelievers are led to wrong thereby: for they make it lawful one year, and forbidden another year, of months forbidden by Allah and make such forbidden ones lawful. The evil of their course seems pleasing to them. But Allah guideth not those who reject Faith.

This prohibition was repeated by Muhammad during the last sermon on Mount Arafat which was delivered during the Farewell Pilgrimage to Mecca on 9 Dhu al-Hijja 10 AH.

When the Qu'ran was first compiled there was only one person who had the last verse of at-Tawba written down: Abi Khuzaima al-Ansari (al-Bukhari 6.478), although it was known and memorized by the companions. [wikipedia]