How sound is the story of Ali ibn Abi Talib, may Allah be pleased with him, abandoning the fight against a disbeliever who spat in his face, saying: "I would have killed him for Allah, but after he spat, my own ego got involved"?

The narration attributed to Ali (may Allah be pleased with him) has not been found and is not considered authentic. It is not permissible to narrate fabricated (or forged) hadiths attributed to the Prophet (peace be upon him) except to expose their falsehood, based on his (peace be upon him) sayings: "Whoever intentionally lies about me, let him take his seat in Hellfire," and "Whoever narrates a hadith from me, believing it to be false, then he is one of the liars." Lying about the Companions is also impermissible due to the general prohibition of lying and because they are the bearers of the religion. As for other weak hadiths, a group of hadith scholars, such as Ibn Mahdi, Ibn al-Mubarak, and Ahmad ibn Hanbal, permitted their narration and acting upon them in matters other than creed and rulings. It is permissible to act upon a weak hadith under certain conditions, and this is the preponderant view, whereas a third group completely prohibited acting upon it.