Leviticus 14:39,40

And the priest shall come again. — If on inspecting it again at the end of the first week’s quarantine, the priest finds that the depression or discolouring has spread in the walls, thus indicating the progress of the disease, just as in the case of leprous men and garments (see Leviticus 13:5), he is to order the affected stones which exhibit these symptoms to be pulled out of the walls, and to be cast into the unclean receptacle which was prepared outside every city for carcases and filth of every kind, just as there was outside the city a clean place for the deposition of the ashes of the sanctuary. (See Leviticus 4:11.) It will be seen that out of the eight verbs used in Leviticus 14:40 in connection with the removing of the affected stones and the constitution of new ones, the scraping, and the plaistering, six are in the plural: viz., they shall take, they shall cast (Leviticus 14:40); they shall pour out, they shall scrape off (Leviticus 14:41); they shall take, they shall put them (Leviticus 14:42); and two are in the singular: viz., he shall take other mortar, he shall plaister (Leviticus 14:42). From this the authorities during the second Temple concluded, and hence enacted, that if the affected stones are in a partition wall which divides two houses occupied by two different owners, both alike must take part in the first six acts, whilst the new mortaring and the plaistering must be done by the owner of the affected house alone.