It is narrated from Qatadah (may Allah have mercy on him), or from another narrator, that Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) saw two men praying: one of them was letting his lower garment hang down, and the other was not completing his bowing and prostration, so he laughed. The people said: "O Abu Abd al-Rahman! What made you laugh?" He said: "I was amazed at these two men. As for the one letting his lower garment hang down, Allah does not look at him; and as for the other, Allah does not accept his prayer."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9334