Ibn `Abbas, Mujahid, `Ikrimah, Ad-Dahhak and several others said that those mentioned in the Ayah are the three who were made to wait to know if their repentance was accepted; Mararah bin Ar-Rabi`, Ka`b bin Malik and Hilal bin Umayyah. Some Companions stayed behind from the battle of Tabuk due to laziness, preferring comfort, ease, ripe fruits and shade. They did not lag behind because of hypocrisy or doubts. Some of them tied themselves to the pillars (of the Masjid) like Abu Lubabah and several of his friends did. Some of them did not do that, and they are the three mentioned here. Those who tied themselves received their pardon before these three men whose pardon was delayed, until this Ayah was revealed,
(Allah has forgiven the Prophet, the Muhajirin and the Ansar...)
(And the three who stayed behind, until for them the earth, vast as it is, was straitened...) We will mention the Hadith about this story from Ka`b bin Malik. Allah said,
(whether He will punish them or will forgive them. ) meaning, they are at Allah's mercy, if He wills, He pardons them or punishes them. However, Allah's mercy comes before His anger,
(And Allah is All-Knowing, All-Wise.) 9:106 Allah knows those who deserve the punishment and those who deserve the pardon. He is All-Wise in His actions and statements, there is no deity worthy of worship nor Lord besides Him.