If meat was left unwatched in an accessible place and may have been moved it becomes rabbinically forbidden unless it can be recognized (63:1-2;1:4). Food of a type that is sometimes Biblically forbidden should not be entrusted to the care of a non-Jew or a person who is suspected of not observing the dietary laws unless it can be recognized or is doubly sealed or marked; if the food is at most rabbinically forbidden a single seal or mark is sufficient, but in both cases there must be no evidence of tampering (118:1-6,8-9;119:1,20). Similar prohibitions apply to utensils that are used with food (see 122:9-10,12). We are lenient about such matters if the person had nothing to gain by switching the food or was at risk of being caught doing so (118:2,5,7,10-13;119:19). On wine or wine utensils that a non-Jew may have had access to see 128-131;136;137:6.
Food or utensils should be acquired only from a person who is known to observe the dietary laws; a person who is suspected of not observing them should not be trusted about the permissibility of food (119:1, and see 2-3 and 122:11; see also 15:3;83:7;86:1-2). A person who is suspected of not observing a particular law must not be trusted even under oath about related laws or about laws that are regarded as less stringent, but may usually be trusted about other matters (119:4-8). A person who is known to be an idolator or to violate the Sabbath publicly or to disbelieve in the words of the sages must not be trusted about anything (119:7). On other types of unobservant people see 119:9-12 and compare 2:1-9. A person who is lenient about something that is generally not regarded as forbidden may be trusted, and a person who observes a stringency that others do not observe may trust others about it (119:7). A trustworthy person is believed that something is permitted if its status is in doubt or if he was in a position to make it permissible, but he is not believed that something is forbidden if its owner contradicts him; see 127:1-4.
If forbidden and permitted things come from separate sources, a thing taken from one of the sources is forbidden if the source cannot be identified even if the permitted sources are in the majority, but a found thing that must have come from one of the sources is in principle permitted because we assume it came from the majority (110:3). Similarly, if an “important” forbidden thing (see Ch.8b) becomes mixed up with a majority of permitted things, anything taken from the mixture is forbidden; but if one of the things is accidentally separated from the mixture, or if something is taken from the mixture before it becomes known that it contains a forbidden thing, it is permitted because we assume it is from the majority; and if the entire mixture becomes scattered it is even permissible to take the things one by one until there are only two left because we assume that each item taken is from the majority (110:5-6; see also 107:1 and 16:12).
In cases involving a Biblical prohibition we rule stringently when doubt arises, but we rule leniently in certain cases of “double doubt” (see 110:4,8-9). If the prohibition is only rabbinical we rule leniently even in cases of “single doubt” when it is possible that the thing in question is not forbidden at all (111:1-6). A mixture is forbidden if the amounts are in doubt; see 98:2-3.
Shulchan Aruch, Copyright (c) 1999 Project Genesis, Inc.