It is narrated from Sayyiduna Ibn Mas'ud (may Allah be pleased with him) that when any one of you performs ruku', he should spread his arms over his thighs and join his two palms together. It is as if I can still see the Prophet's (peace and blessings be upon him) fingers spread apart. Saying this, he demonstrated by joining his two palms together in the position of ruku'. (This ruling has been abrogated.)