From a long narration on Maqtal of Imam Husain (ع) narrated by Imam Sadiq (ع) from His Father, from Imam Ali ibn Husain (ع):

فبلغ ذلك الحسين (عليه السلام)، فهم بالخروج من أرض الحجاز ألى أرض العراق، فلما أقبل الليل راح إلى مسجد النبي (صلى الله عليه وآله) ليودع القبر، فلما وصل إلى القبر سطع له نور من القبر فعاد إلى موضعه، فلما كانت الليلة الثانية راح ليودع القبر، فقام يصلي فأطال، فنعس وهو ساجد، فجاءه النبي (صلى الله عليه وآله) وهو في منامه، فأخذ الحسين (عليه السلام) وضمه إلى صدره، وجعل يقبل بين عينيه، ويقول: بأبي أنت، كأني أراك مرملا بدمك بين عصابة من هذه الامة، يرجون شفاعتي، مالهم عند الله من خلاق، يا بني إنك قادم على أبيك وامك وأخيك، وهم مشتاقون إليك، وإن لك في الجنة درجات لا تنالها إلا بالشهادة. فانتبه الحسين (عليه السلام) من نومه باكيا، فأتى أهل بيته، فأخبرهم بالرؤيا وودعهم، وحمل أخواته على المحامل وابنته وابن أخيه القاسم ابن الحسن بن علي (عليهم السلام)، ثم سار في أحد وعشرين رجلا من أصحابه وأهل بيته، منهم أبو بكر بن علي، ومحمد بن علي، وعثمان بن علي، والعباس بن علي، وعبد الله بن مسلم بن عقيل، وعلي بن الحسين الاكبر، وعلي بن الحسين الاصغر

When Imam Husain (ع) heard of this (ِi.e. Yazid ordering killing the Imam), He was determined to leave the land of Hijaz heading towards the land of Iraq. As nighttime befell, the Imam went to the Mosque of the Prophet (ص) to bid farewell. When he got to the grave, a bright light radiated from the grave, so the Imam returned back."

"On the second night, he went to the Mosque to bid farewell to the grave. He began to pray lengthy prayers so He fell asleep as he was in the state of prostration and saw the Prophet (ص) in His dreams. The Prophet (ص) took al-Husain (ع) and hugged him, and began to kiss his forehead and said:

"May my father be sacrificed for You! It is as if I see You covered in Your own blood, killed by a group from this nation who seek my intercession (Shifaat). They will not see anything from the mercy of Allah! O' son you are coming towards your father, mother, and brother and they are longing for you. And for you, there are such ranks/status in heaven that you cannot attain except through martyrdom."

Then Imam Husain (ع) then woke up crying. He went to His household and informed them of what happened in that dream and bid farewell to them.

He took His sisters, His daughters and the son of His Brother al-Qasim bin al-Hasan bin Ali (ع), alongside 21 from His companions and members of His household, among them were:

Abu Bakr bin Ali, Muhammad bin Ali, Uthman bin Ali, al-Abbas bin Ali, Abdullah bin Muslim bin Aqil, Ali bin al-Husain al-Akbar, and Ali bin al-Husain al-Asghar.

[Source: al-Amali, Shaikh Sadooq, Pg. 216-217]