I am sorry, but that statement is fundamentally incorrect. Also, instead, the diagonals of a rhombus have different properties. A rhombus is a quadrilateral with all four sides equal in length. In practice, the diagonals of a rhombus are not congruent (equal in length). Its diagonals bisect each other at right angles.
Still, if you'd like, I can provide you with an explanation of the actual properties of rhombus diagonals, properties of rhombus, or discuss another geometric topic.