Al-Matalib al-'Aliyah 1921 — The martyrs

It is narrated from Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) that he said: I was with the Prophet (peace and blessings be upon him) in the Cave of Thawr, and at that time he (peace and blessings be upon him) made this supplication: 'Allahumma ta'nan wa ta'unan' (O Allah, (grant my Ummah death by) the thrust of spears and plague). I said: "O Messenger of Allah (peace and blessings be upon him), I know that you have asked for the ways of death for your Ummah. As for the wounds of spears (martyrdom on the battlefield), we know them, but what is this plague?" He (peace and blessings be upon him) said: "It is a kind of tumour or infection that forms in the inner part of the body, like a boil. If your life is prolonged, you will soon see it."
The chain of this hadith is extremely weak and unreliable because of the narrator named Ja'far bin al-Zubayr.