(He turned in mercy also) to the three who were left behind; (they felt guilty) to such a degree that the earth seemed constrained to them, for all its spaciousness, and their (very) souls seemed straitened to them,- and they perceived that there is no fleeing from Allah (and no refuge) but to Himself. Then He turned to them, that they might repent: for Allah is Oft-Returning, Most Merciful. (118)
Tafsir
A third group consisted of those who were left behind. These were three youths, Ka‘b ibn Malik, Mararah ibn Rubay and Hilal ibn Umayyah. Though they regarded their inability to proceed on this journey as a shortcoming, their feelings of repentance and turning towards God had not been as intense as was required in this first stage. That is why they were punished by a social boycott. Now even with this boycott these three had a number of options. They could have remained happy and contented; they could have remained engrossed in their homes and gardens; they could have become rebellious; they could have formed their own separate group in collaboration with disgruntled elements, thus forming an island, a happy world cut off from the general body of Muslims. But they refrained from doing so. The thought of having earned the displeasure of God and His Prophet disturbed their minds so greatly that they failed to find a moment’s peace. For them this was an option, not a compulsion. For they could have escaped by rebelling against this boycott and joining any other group. But their response being positive, they naturally turned to God for forgiveness. They repented and prayed to God. Their hearts were truly softened. After a period of 50 days of prayer God showed them His mercy and they were pardoned.
Alternatively, you may use the smart search feature provided below