Whenever Imam Ali (AS) delivered sermons, he used to say: Ask me before you cannot see me again!

Swear to God that you do not ask me about any of the past or the present events, unless I am aware of them. Suddenly Sa’ad ibn Abi Waqqas stood up and asked: O’ Amiral Momeneen, inform me how many hairs are there in my head and beard? Imam Ali (AS) replied: Swear to God; know that the question you asked me, the Prophet of Islam (PBUH) informed me that you would ask such a question. There is no hair in your head and beard unless there is a Satan sitting in its root. And without a doubt there is a wicked and evil one in your house that will kill my son Hussain (AS)! And Omar ibn Sa’ad at that time was a child who was running in front of his father [1].

[1] Beharul Anwaar, Vol. 9, Page 635.

Source: en.shafaqna.com