It is narrated from Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) that he said: "If only I had asked the Messenger of Allah (peace and blessings be upon him) about three things, that would have been dearer to me than red camels: (first,) who would be the caliph after him? (Second,) about people who say: We acknowledge that zakah is due on our wealth, but we will not pay it to you; is it lawful to fight them? And (third,) about kalalah (one who leaves neither parent nor child)." This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), and they did not record it.