Is freedom a condition for the obligation of Jihad?

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Freedom is a condition for the obligation of Jihad. This is established by the report that the Prophet (peace be upon him) pledged allegiance to a free man for Islam and Jihad, but pledged allegiance to a slave only for Islam, excluding Jihad. Furthermore, Jihad is an act of worship requiring travel, and therefore it is not obligatory upon a slave, similar to Hajj.