Is the Hadith, "There is no prayer for a concealer (katim)," authentic, and what does it mean?

There is no Hadith with this exact wording. However, it is narrated in Sahih Muslim on the authority of 'Aisha that the Prophet, may Allah's prayers and peace be upon him, said: "There is no prayer in the presence of food, nor when one is being pressed by the two impurities." The two impurities are urine and feces, and perhaps this is what is intended by the wording mentioned.