On the eve of the 10 day of Muharram (Tasu'ah - coming from the ordinal number nine), Imam Hussein knew that this will be the last night for him to spend the night with family and companions.  

Early at night Imam Husain (PBUH) gathered his companions. After praising God, he told them: "I cannot find companions more allegiant and better than my companions and I cannot find a household kinder and more helpful than my household. May God reward you!" He went on to say: "I think this was the last opportunity that these people gave to us. Be aware that I give you the permission to leave me. So you can go since you are no longer under my allegiance. Now that it is dark everywhere, you can leave with a horse."

At this time, Imam Husain's (PBUH) household and then his companions gave valiant speeches and announced their fidelity to him. They emphasized that they will risk their lives to stay with him. Some historical sources and maqtals reported some of these speeches.

However later that night, Abbas b. Ali (a) was in charge of protecting the camps of Imam Husain (PBUH) family. Although there was not supposed to be a battle that night, 'Abbas (a) took caution to watch the camps during the night. He was accompanied by Zuhayr b. Qayn.
 

According to some sources, Burayr b. Khudayr al-Hamdani asked Imam Husain (PBUH) permission to go to 'Umar b. Sa'd and admonish him. Imam Husain (PBUH) gave him the permission.

Burayr went to 'Umar b. Sa'd; he entered 'Umar's camp and sat there without saying hello. 'Umar was irritated by Burayr's treatment and told him: "O' the Hamdani brother! What made you not say hello to me? Am I not a Muslim? Do I not know God and his Prophet (s) and do I not testify the truth?"
 

Burayr replied: "If you knew God and the Prophet (s), as you claim, you would not determine to kill the Prophet's (s) household. What is more, this is the clear water of Euphrates with its waves twisting like snakes, from which animals in Iraq drink, while Husain (PBUH), his brothers, women and household are dying from thirst. You have denied them the water, and yet you think you know God and the Prophet (s)?"
 

'Umar b. Sa'd replied after a moment of reflection: "Burayr! I swear to God that whoever fights with them and usurps their rightful place will end up in the Hell, but do you want me to leave the rule of Rey to someone else? I swear to God that I cannot accept this."
 

He then said: "I was asked by 'Ubayd Allah b. Ziyad to undertake this task. I swear to God that I am stuck in a dilemma: should I abandon the rule of Rey, which has always been my dream, or should I commit the sin of killing Husain? There is a fire in killing al-Husayn that cannot be stopped, but the rule of Rey is so much as a dream."

Burayr went back to Imam Husain (PBUH) and told him: "O' the son of the Prophet (s)! 'Umar b. Sa'd would rather kill you than abandon the rule of Rey."

During the night before Ashura, Nafi' b. Hilal noticed that Imam Husain (PBUH) went out of his camp, on his own, to inspect the hills around. Nafi' followed Imam (a). When Imam (a) noticed the presence of Nafi', he told him: "Why did you come out of your camp?" Nafi' replied: "O' the son of the Prophet (s)! I am worried about your life especially when you show up to this cruel army." Imam (a) said: "I have come out to inspect the ups and downs of this field before tomorrow's war breaks", said Imam Husain (PBUH). When the inspection was all done, Imam Husain (PBUH) told Nafi': "Do you not want to disappear in this dark night to save your life?" Nafi' fell on Imam Husain (PBUH) feet and replied: "I have a sword that is worth one thousand dirhams and I have a horse that is worth about one thousand dirhams. I swear to God who privileged and honored me to be here that I would never leave you alone so long as my sword can cut".

After this dialogue, Imam al-Husayn (a) went tohis sister, Zaynab's (a) tent. Nafi' b. Hilal stayed outside waiting for Imam (a). He overheard the Lady Zaynab (a) saying to Imam (a): "Have you put your companions to test? I am worried about them betraying us and surrendering you to the enemy". Imam al-Husayn (a) replied: "I swear to Godthat I have tested them. They are brave people who look at death with the corner of their eyes and they love to die for me just as an infant loves its mother's breast".
 

Nafi' thought that Imam al-Husayn's (a) household may have concerns about the faithfulness and perseverance of Imam's (a) companions. So he went to Habib b. Muzahir and talked to him about the concerns of Imam's (a) households. They decided to go to Imam al-Husayn (a) and his households to ensure them that they will defend them until the last breath of their lives.
 

Habib b. Muzahir called Imam's (a) companions and told Banu Hashim to return to their camps. He then told the remaining people what he had heard from Nafi'. They all said: "We swear to God—who privileged and honored us to be here—that we would attack the enemy had we not been waiting for Imam al-Husayn's (a) command".
 

Habib b. Muzahir and other companions of Imam al-Husayn (a) approached the camps of Imam's (a) households with their drawn swords and said: "O' the household of the Prophet (s)! These are the swords of your men that will not go back to the sheath unless they kill your enemies. These are your men's spears, and they swear to push them into your enemy's breasts".
 

On the evening of Tasu'a, 'Umar b. Sa'd ordered his army to break the war against Imam al-Husayn (a) and his companions. When Imam al-Husayn (a) found out about the order, he told his brother, 'Abbas b. Ali (a): "if possible, convince them to postpone the war until tomorrow so that we can have the opportunity to pray to God. Only God knows how much I love to pray and recite the Qur'an."
 

According to some sources, Imam al-Husayn (a) and his companions spent the night performing prayers and orisons.