Abbas - Tanwîr al-Miqbâs min Tafsîr Ibn ‘Abbâs
(Then, when the sacred months have passed) then after the day of immolation when the month of Muharram passes, (slay the idolaters) whose treaty is for fifty days (wherever ye find them) whether in the Sacred Precinct or outside it, during the sacred months or at any other time, (and take them (captive)) imprison them, (and besiege them) in their homes, (and prepare for them each ambush) on every road they tread for trade. (But if they repent) from idolatry and believe in Allah (and establish worship) and acknowledge the five daily prayers (and pay the poor-due) acknowledge the payment of the poor-due, (then leave their way free) if they wish to go to the House of Allah. (Lo! Allah is Forgiving) He forgives whoever repents, (Merciful) towards whosoever dies in a state of repentance.
Then, when the sacred months have passed — that is, [at] the end of the period of deferment — slay the idolaters wherever you find them, be it during a lawful [period] or a sacred [one], and take them, captive, and confine them, to castles and forts, until they have no choice except [being put to] death or [acceptance of] Islam; and lie in wait for them at every place of ambush, [at every] route that they use (kulla, ‘every’, is in the accusative because a [preceding] genitive-taking preposition has been removed). But if they repent, of unbelief, and establish prayer and pay the alms, then leave their way free, and do not interfere with them. God is Forgiving, Merciful, to those who repent.
Mujahid, `Amr bin Shu`ayb, Muhammad bin Ishaq, Qatadah, As-Suddi and `Abdur-Rahman bin Zayd bin Aslam said that the four months mentioned in this Ayah are the four-month grace period mentioned in the earlier Ayah,
فَسِيحُواْ فِى الاٌّرْضِ أَرْبَعَةَ أَشْهُرٍ
(So travel freely for four months throughout the land.) Allah said next,
فَإِذَا انسَلَخَ الأَشْهُرُ الْحُرُمُ
(So when the Sacred Months have passed...), meaning, `Upon the end of the four months during which We prohibited you from fighting the idolators, and which is the grace period We gave them, then fight and kill the idolators wherever you may find them.' Allah's statement next,
(And fight not with them at Al-Masjid Al-Haram, unless they fight you there. But if they attack you, then fight them. )2:191 Allah said here,
(and capture them), executing some and keeping some as prisoners,
وَاحْصُرُوهُمْ وَاقْعُدُواْ لَهُمْ كُلَّ مَرْصَدٍ
(and besiege them, and lie in wait for them in each and every ambush), do not wait until you find them. Rather, seek and besiege them in their areas and forts, gather intelligence about them in the various roads and fairways so that what is made wide looks ever smaller to them. This way, they will have no choice, but to die or embrace Islam,
(But if they repent and perform the Salah, and give the Zakah, then leave their way free. Verily, Allah is Oft-Forgiving, Most Merciful.) Abu Bakr As-Siddiq used this and other honorable Ayat as proof for fighting those who refrained from paying the Zakah. These Ayat allowed fighting people unless, and until, they embrace Islam and implement its rulings and obligations. Allah mentioned the most important aspects of Islam here, including what is less important. Surely, the highest elements of Islam after the Two Testimonials, are the prayer, which is the right of Allah, the Exalted and Ever High, then the Zakah, which benefits the poor and needy. These are the most honorable acts that creatures perform, and this is why Allah often mentions the prayer and Zakah together. In the Two Sahihs, it is recorded that Ibn `Umar said that the Messenger of Allah said,
(I have been commanded to fight the people until they testify that there is no deity worthy of worship except Allah and that Muhammad is the Messenger of Allah, establish the prayer and pay the Zakah.) This honorable Ayah (9:5) was called the Ayah of the Sword, about which Ad-Dahhak bin Muzahim said, "It abrogated every agreement of peace between the Prophet and any idolator, every treaty, and every term.'' Al-`Awfi said that Ibn `Abbas commented: "No idolator had any more treaty or promise of safety ever since Surah Bara'ah was revealed. The four months, in addition to, all peace treaties conducted before Bara'ah was revealed and announced had ended by the tenth of the month of Rabi` Al-Akhir.''
Maududi - Sayyid Abul Ala Maududi - Tafhim al-Qur'an
Here "the months made unlawful" are not those four months during which war is forbidden for the sake of Haj and `Umrah but the four months that were made unlawful for the Muslims to make any attack on the mushriks, who were granted respite by v. 2.
That is, "Mere repentance from disbelief and shirk will not end the matter. but they shall have to perform the prescribed prayer and pay Zakat dues. Without these it will not be considered that they had given up disbelief and embraced Islam. " Hadrat Abu Bakr based his decision on this verse in the case of the apostates, after the death of the Holy Prophet, who argued that they were not the rejecters of Islam, because they offered Salat, even though they had refused to pay the Zakat dues. This argument roused doubts in the minds of the Companions in general that they had no right to fight with such people as these. But Hadrat Abu Bakr removed their doubts, saying, "Verse 5 enjoins us to let those people go their way who fulfill all the three conditions- repentance from shirk, the establishment of Salat and the payment of Zakat. We cannot forbear them, because they do not fulfill one of these three conditions."
That is, "if during a fight, an enemy makes a request that he should be given an opportunity to understand Islam, the Muslims should give him a surety of protection and allow him to visit them. They should then present Islam before him in order to make him understand it. If, after this, he does not embrace Islam, they should convey him safely to his place". Such a person who comes to Dar-ul-Islam under the above mentioned protection is called musta'min in the Islamic Code.