1. The opening Takbir
2. Going down for Ruku’
3. Coming back up from Ruku’
Most of the authentic narrations mention these three places only, without a fourth place, and this is what Imam Ahmad (r) went with.
This answer was collected from The Hanbali Madhhab website. The answers to the questions are given by Imam Zahed Fattah in accordance to the Hanbali School of Jurisprudence.