Kitab-i-Aqdas/Elder72

It is unlawful for you to buy or sell maid-servants and youths. One creature must not purchase another, since this is prohibited in the Tablet of God. Thus was the matter inscribed by the Pen of Justice through Grace.

No one should glory over another. All are slaves to Him and guides to the truth that "there is no god but He". He is the One who is wise about everything.