and he (ṣallá Allāhu ʿalayhi wa-sallam) would command the completion of bowing and prostration, and he would liken those who do not do so to a hungry person who eats one or two dates which do not satisfy him at all. He would say about this: "Indeed, he is among the worst of thieves." He would declare the prayer of one who does not straighten his back in bowing and prostration to be invalid, as detailed previously in (bowing). He instructed the one who performed his prayer poorly to have tranquility in prostration, as mentioned at the beginning of the chapter on the supplications of prostration