When the matter of Imam Husayn (a.s.) reached here, Ubaydullah called Umar bin Sa’ad and said, “Go and confront Husayn and after accomplishing our task, return back to your position.” Umar bin Sa’ad tried to excuse himself when Ubaydullah said, “Very well, then you may return back what has been conferred upon you.”
When Ubaydullah said this Umar replied, “Give me respite for today so that I may take a decision”, saying this he left and asked the opinion of his well-wishers, all of whom advised him to refrain from it. His nephew Hamza bin Mugheera bin Sha’bah came to him and said, “I request you in the name of Allah not to confront Husayn, for by doing this you will be sinning and severing the bonds of relationship with him. By Allah! Even if you have to leave this world, the wealth and the kingdom upon the earth, it is better for you than go to the presence of the Almighty Allah with the blood of Husayn upon your neck.”
Umar replied that he would not do so and he spent the entire night pondering upon it saying, “Could I decline the governorship of Ray, while it is my dream, or should I return back blamed for killing Husayn? Should I kill him, then I will wind up in the hell from which there is no escape, while the governorship of Ray is the refreshment of my eyes.”
Then he returned to Ubaydullah and said, “You have deputed me for this task and all the people have heard it. If you desire send me for this job, otherwise send someone else against Husayn from the noblemen of Kufa, who would be better than me”, then he named some of them. Ubaydullah replied, “If I have to send someone else I will not ask your opinion, then now if you are ready to go to Karbala with the command over our army, do so, or else return back the post which we have conferred upon you.” Hearing this Umar replied, “I myself will go”, saying this he proceeded until he encamped opposite Imam Husayn (a.s.).
Reference : Nafasul Mahmoom – Shaikh abbas Qummi (r.a.)