Luke 2:43

43 and when they had fulfilled the days, as they were returning, the boy, Jesus, stayed behind in Jerusalem. Joseph and his mother didn't know it,

Luke 2:43 In-Context

41 His parents went every year to Jerusalem at the feast of the Passover.
42 When he was twelve years old, they went up to Jerusalem according to the custom of the feast,
43 and when they had fulfilled the days, as they were returning, the boy, Jesus, stayed behind in Jerusalem. Joseph and his mother didn't know it,
44 but supposing him to be in the company, they went a day's journey, and they looked for him among their relatives and acquaintances.
45 When they didn't find him, they returned to Jerusalem, looking for him.
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