What kind of prostration was it?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It is similar to the prostration (sujūd) in prayer, and this is the more apparent view.
2. It was a bowing and inclining similar to the bowing (rukūʿ) in prayer.