Even the mercy of Mercifulness...
Even the mercy of Mercifulness, of whose manifestations is the guidance of all guides on the road of tawhīd , covers all, except those who were diverted from the disposition of rectitude, and, owing to their own ill-selection, prevented themselves from being benefited by it, not that the Mercifulness did not cover them.
Even in the Hereafter world, which is the day of harvesting the bad and good cultivations, those who have bad cultivations are inevitably short of being benefited by the mercy of the Merciful.
To be short, the sālik who wants his tasmiyah to be implemented, will have to convey Allah's mercies to his heart to have it believe in the favors of the Beneficent and the Merciful, which is marked out on the heart by his looking with kindness and leniency at the servants of Allah, desiring goodness and righteousness to all of them.
This look is that of the great prophets and the perfect holy men [ awliyā' ] (' a ), although they had two looks: one for welfare and the happiness of the community, the system of the family and the regime of the Virtuous City, and the second for the happiness of the individual. They were very much concerned about the happiness of these two. The divine laws, which are established, disclosed, enforced and carried out by them, take complete care of the happiness of those two.
Even in carrying out penalties and punishments and the like, which seem to have been coined in conformity with the laws of the Virtuous City, the happiness of both are taken into consideration, because these affairs are mostly for educating the soul and bringing it to happiness. Even those who had no light of faith and happiness, and were killed by the fighters in jihād and the like, such as the Jews of Banū Qurayzah, this killing (being killed) was for their goodness and reformation.
It can be said that killing them was of the complete mercy of the Seal of the Prophets ( s ), because by their survival in this world they would prepare every day diverse punishments for themselves, while the whole life in this world cannot be compared with the tortures and the hardships of a single day in the Hereafter. This is quite obvious to those who have knowledge about the extent of the tortures and punishments in the Hereafter and their reasons and causes.
So, the sword that was put to the necks of the Jews of Banū Qurayzah and their like was nearer to the horizon of mercy than to the horizon of anger and wrath.