Prophet Muhammad would always forgive non-Muslims - ALLAH Almighty has described Prophet Muhammad (peace be upon him) as a “Mercy for all the Worlds,” as He said in the Qur’an: “We have sent you as a mercy for all the worlds.” (Qur’an, 21:107)
This means that the Prophet’s characteristic of being merciful was not just limited to the Muslim Ummah or nation, but it also extended to non-Muslims, despite the fact that some of them (non-Muslims) made every effort to harm the Prophet and his mission. This mercy and forgiveness are clearly demonstrated in several instances when the Prophet (peace be upon him), despite having opportunities to take revenge, never did so and always forgave even his staunch enemies.
Ayesha said that the Prophet (peace be upon him) never took revenge on his own behalf on anyone. She also said that he never returned evil for evil, but he would forgive and pardon. This will, God willing, become clear after a deep analysis of the following accounts of his life.
In the earlier portion of his mission, the Prophet (peace be upon him) traveled to the city of Taif, a city located in the mountains nearby to Makkah, in order to invite them to accept Islam. The leaders of Taif, however, were rude and discourteous in their treatment of the Prophet (peace be upon him).
Not being content with their insolent attitude toward him (peace be upon him), they even encouraged unruly urchins of the town to abuse and harass the Prophet (peace be upon him). The riffraff followed the Prophet shouting at and abusing him, and throwing stones at him, until he was compelled to take refuge in an orchard.
Thus the Prophet (peace be upon him) had to endure even more obstacles in Taif than he had had to face in Makkah. These ruffians, stationed either side of the path, threw stones at him until he was deeply injured with his shoes smeared with blood.
These oppressions so grievously dejected the Prophet and plunged him into in such a state of depression that a prayer, citing his helplessness and pitiable condition and seeking the aid of God, spontaneously came from his lips: “O God, to You I complain of my weakness, lack of resources and humiliation before these people. You are the Most Merciful, the Lord of the weak and my Master. To whom will You consign me? To one estranged, bearing ill will, or an enemy given power over me? If You do not assign me any worth, I care not, for Your favor is abundant upon me. I seek refuge in the light of Your countenance by which all darkness is dispelled and every affair of this world and the next is set right, lest Thy anger should descend upon me or Your displeasure light upon me. I need only Your pleasure and satisfaction for only You enable me to do good and evade the evil. There is no power and no might but You.”
The Lord then sent the angel of mountains, seeking the permission of the Prophet (peace be upon him) to join together the two hills and crush the city of Taif, between which it was located. Out of his great tolerance and mercy, the Messenger of God replied, “No! For, I hope that God will bring forth from their loins people who will worship God alone, associating nothing with Him.” (Saheeh Muslim)
His mercy and compassion was so great that on more than one occasion, God, Himself, reprimanded him for it. One of the greatest opponents of Islam and a personal enemy, was Abdullah bin Ubayy, the leader of the hypocrites of Madinah. Outwardly proclaiming Islam, he surreptitiously inflicted great harm to the Muslims and the mission of the Prophet (peace be upon him).
Knowing his state of affairs, the Prophet Muhammad (peace be upon him) still offered the funeral prayer for him and prayed to God for his forgiveness. The Qur’an mentions this incident in these words: “And never (O Muhammad) pray for one of them who dies, nor stand by his grave. Lo! They disbelieve in God and His Messenger, and they died while they were evil doers.” (Qur’an, 9:84)
Abdullah bin Ubayy worked all his life against the Prophet Muhammad (peace be upon him) and Islam and left no stone unturned so as to bring him into disrepute and try to defeat his mission. He withdrew his three hundred supporters in the battle of Uhud and thus almost broke the backbone of the Muslims at one stroke. He engaged in intrigues and acts of hostility against the Prophet of Islam and the Muslims. It was he who tried to bring shame to the Prophet by inciting his allies to falsely accuse the Prophet’s wife, Ayeha, of adultery in order to discredit him and his message.
source : islamreligion.com