Is spreading rumors circulating about an unmarried girl being pregnant, which a person heard and mentioned to others, considered slandering chaste women (qadhf al-muhsanat) and a major sin (kabirah), especially if the one spreading the rumor is unaware of the truth of the matter?

What you did, delving into the girl's honor by spreading what people say about her, is forbidden. It is one of the greatest and most heinous major sins. Allah Almighty condemned this behavior in His saying: "When you received it with your tongues and spoke with your mouths that of which you had no knowledge, and you thought it was insignificant, while with Allah it was great." This act is not slander (qadhf); rather, it is forbidden backbiting (gheebah), because it is relaying what people say, not a direct accusation. Backbiting is one of the major sins. You must hasten to repent, and remember the words of the Messenger of Allah, peace and blessings be upon him: "O community of those who have submitted with their tongues but in whose hearts faith has not entered, do not harm Muslims, nor shame them, nor seek out their faults. For indeed, whoever seeks out the fault of his Muslim brother, Allah will seek out his fault, and whoever Allah seeks out his fault, He will expose him, even if he is in the confines of his own home."