Whether in the past, future, or present, all those who purify their almsfood do so by continually checking in this way. So, Sāriputta, you should all train like this: ‘We shall purify our almsfood by continually checking.’” That is what the Buddha said. Satisfied, Venerable Sāriputta approved what the Buddha said.

Middle Discourses 152 The Development of the Faculties