Prostrate is an adjective meaning lying face down, and a verb (usually reflexive) meaning to put or throw face down. Prostate is a noun denoting a gland in male mammals that controls the release of urine and creates a milky fluid that constitutes a large percentage of the volume of semen.
Confusing these two words can lead to unfortunate results—for example:
He lay prostate before Archbishop Milingo and four other bishops … [Daily Nation]
. . . men 40 to 65 years old are invited to take advantage of a free prostrate screening clinic to be held at the Bamberg Job Corps Center. [The TandD]
And as sure as the sun rises from the east, the thief would prostate himself before the wise ones, plead guilty and beg for forgiveness. [The Standard]
These writers use prostate and prostrate correctly:
The Fiver’s never been one to prostrate itself before the altar of the Big Buck and acquiesce to the wishes of sponsors. [Guardian]
The Da Vinci surgical robot made by Intuitive Surgical is changing the way many doctors perform surgeries like prostate removal. [Forbes]
He jokes that Muslims do their public image no favor by prostrating themselves in their daily worship. [New York Daily News]

