How authentic is the Hadith: "Hussein is from me and I am from Hussein," and what is the meaning of its second part: "and I am from Hussein"?

It was authentically reported from the Prophet (peace and blessings be upon him) that he said: "Hussain is from me, and I am from Hussain. Allah loves whoever loves Hussain. Hussain is a grandson among the grandsons." The meaning of this is that there is a union and connection between them. It is as if the Prophet (peace and blessings be upon him), knowing through the light of revelation what would happen, singled him out for mention and clarified that they are like one entity in the obligation of love and the حرمة (prohibition) of exposure and hostility. And that loving Hussain is loving the Messenger, and loving the Messenger is loving Allah.