A retention assembly for captivating a shackle assembly on a loop of a conventional wire rope sling assembly and preventing removal of the shackle assembly. A thimble member has first and second legs forming a loop, and at least one aligned transverse bore extending through each of the first and second legs of the thimble member. A shackle member is partially installed through the loop of the thimble member. Thereafter, a retaining member is secured within the aligned bores of the first and second leg, extending across the loop, and preventing withdrawal of the shackle member from the loop without observable damage to the shackle, thimble, retaining member , sling assembly or combinations thereof.