While I'm a "don't believe in spanking", mama, everyone parents differently and reasonable spanking is a personal choice. I would document the date and words said for future reference and just keep an eye on the situation. Look for new AND fading bruises in the same area which points to repeated injury to the same area. Spanking should never leave bruising anyways. Just be alert to what you heard, document and report future findings if you begin to see a pattern.