What is the correct narration concerning the Aqiqah offering regarding the head treatment?

Primary text

The narration stating 'wa yusamma' (and he is named) is considered sounder than the narration stating 'wa yudamma' (and he is bloodied) concerning the newborn's seventh day. Al-Shafi'i narrated this as the correct understanding, and Ahmad considered the narration mentioning 'yudamma' to be an error, possibly a scribal mistake.