Mishná sobre Negaim 2:6

Everyone can become impure from negaim, except for a non-Jew and a resident alien. All are qualified to inspect negaim, but only a priest may declare them unclean or clean. He is told, "Say: 'unclean,'" and he repeats "unclean," or "Say: 'clean,'" and he repeats "clean." Two negaim may not be inspected simultaneously whether in one man or in two men; rather he inspects one first and isolates him, certifies him as unclean or pronounces him clean, and then he inspects the second. One who is isolated may not be isolated again nor may one who is certified unclean be certified unclean again. One who is certified unclean may not be isolated nor may one who is isolated be certified unclean. But in the beginning, or at the end of a week, he may isolate on account of the one nega and isolate him on account of another one; he may certify him unclean on account of one sign and also certify him unclean on account of another sign; he may isolated the one sign and declare the other clean, or certify the one unclean and declare the other clean.