In Hindi, a subjunctive verb form can be used to indicate a third person imperative. There are no third person imperatives in English, so some ingenuity is required to translate these imperatives.
चोट न लग जाये! – “Don’t let (someone) get hurt!” (This could be a warning said about a child, etc.)
गिर न जाए! – “Don’t let (someone) fall!”
बच्चे सड़क पर न खेलें – “Make sure the children don’t play on the street”
जिसने कभी पाप न किया हो वह पहला पत्थर मारे – “Let the one who has never sinned cast the first stone”
This idiom is generally used when issuing a warning (e.g. चोट न लग जाये) or when the person commanded is unknown and therefore cannot be addressed with a second person imperative (e.g. जिसने कभी पाप न किया हो वह पहला पत्थर मारे).