Urea is present mainly in the urine of all mammals, but it also occurs in blood, bile and milk. Urea is naturally produced during the process of breakdown of proteins. Due to this process, amino groups are removed from the amino acid present in the proteins. These amino groups are converted to highly toxic ammonia (NH3), and the ammonia thus produced is finally converted to urea by the liver. The urea thus formed then passes to the kidneys and is finally excreted from the body through the urine.
This video explains how to detect the presence of urea in the given sample of urine.