3 fold rule
According to one passage in the Tipitaka, the Buddha allowed eating meat for monks, if it is clear that the animal was not killed on purpose, especially to provide the meal.
Majjhima Nikaya 55.5
The passage reads as follows: "I say that there are three instances in which meat should not be eaten: when it is seen, heard, or suspected that the living being has been slaughtered for the bhikkhu. I say that meat should not be eaten in these three instances. I say that there are three instances in which meat may be eaten: when it is not seen, not heard, and not suspected, that the living being has been slaughtered for the bhikkhu."
Lay people
The threefold rule specifies conditions under which meat could be eaten by monastic monks and nuns, but there is no indication if this rule applies to lay people. Thus, there has been controversy over if Buddhists should eat meat or not. The context of the passage and who it is addressed to indicate that the rule was meant for monastics only. The First Precept further stipulates against killing or causing to kill and lay people do make a decision when purchasing meat from a butcher or grocery store.