Is what was narrated from Imam Ja'far al-Sadiq (peace be upon him) regarding the death of two-thirds of the world's population (one-third by disease and one-third by war) before the appearance of Imam al-Mahdi (may Allah hasten his reappearance) correct?

The narration about the death of two-thirds of the Earth's inhabitants before the appearance of the Mahdi is among the Shia narrations that are not given attention due to their leniency in transmitting narrations and the widespread falsehoods within them, especially what is attributed to Ja'far al-Sadiq.

Nu'aym ibn Hammad narrated in "Al-Fitan" from Ali ibn Abi Talib, may Allah be pleased with him, that he said: "The Mahdi will not emerge until one-third is killed, one-third dies, and one-third remains." However, the chain of transmission for this narration is very weak, as it includes Kaysan al-Ru'asi al-Qassar, Yazid ibn Bilal, and Yahya ibn Yaman, all of whom are weak or have weakness in them.

A sound narration has been transmitted about the scarcity of Arabs at the end of time, at the emergence of the Dajjal, not the Mahdi, where the Prophet, peace and blessings be upon him, said: "They will be few on that day, and most of them will be in Bayt al-Maqdis (Jerusalem), and their Imam will be a righteous man."