Mu'awiya summoned Musa and asked him how much money his...
Mu'awiya summoned Musa and asked him how much money his father had spent to buy these individuals, he replied 30,000 dirhams". Why did Imam Hussain (as) refuse to give bay'a to Yazeed? Abu Sulaiman claims: Ansar.org states:Ibn Al-Zubair and Al-Hussain (as) disagreed on this allegiance but it does not defame this allegiance because it must have some objectors. From this we know that Mu'awiyah was eager to have the acceptance of the Ummah in giving the allegiance to Yazeed.
The objection was not some simple matter like a difference of opinion over a dinner table. This was a matter intrinsically linked to the Deen (religion), that ultimately asks the question, 'was it legitimate for a fasiq to be the khalifa of Rasulullah (s)?' On the one hand we had the opinion of IbnUmar who deemed it correct, and on the other we had Imam Hussain (as) who said that this was a sin in the eyes of Allah (swt).
The clearest proof comes from his letter to the Shi'a of Kufa: "From Husayn b. Ali to the believers and the Muslims. Hani and Sa'id came to me with your letters, they being the last among your messengers and delegations to come to me. I have understood what you said and that you have invited me to come to you because you have no Imam to guide you, and that you hope my arrival there will unite you in the right path and in the truth.
I am sending my cousin and the trusted one from my family [Muslim b. Aqil] to report to me about your affairs. If his report conforms with what you have written, I will soon come. But you must be clear about the fact that the Imam is only one who follows the Book of God, makes justice and honesty his conduct and behaviour, judges with truth, and devotes himself to the service of God.
Peace." (Tareekh Tabari Volume 2 page 235) The last sentence of the letter, explaining the duties of an Imam and the nature of the Imamate, helps us to understand Husayn's approach and attitude towards the whole problem. The Imam was one who: Followed the Quran and Sunnah Was just and trustworthy Was of good character Was a true devotee of Allah (swt) It is evident that Imam Hussain (as) did not see these conditions inherent in Yazeed which is why he refused to give him baya.
Tabari also records this letter of Imam Hussain (as) to the Shi'a of Basra: "God has chosen Muhammad from among his people, graced him with His Prophethood and selected him for His message. After he admonished the people and conveyed His message to them God took him back unto Himself.