I read in Ajahn Brahms book that you pass through 4 immaterial realms after jhanas and before enlightenment. I want to know more about them. Where can I find the suttas in the Tripitaka?
The immaterial jhana are optional & not required for enlightenment (refer to SN 12.70), which is why immaterial jhana are not included in the noble eightfold path (refer to SN 45.8). The Buddha attained enlightenment by developing the 4th material jhana (refer to MN 19). However, the immaterial jhana are described in many suttas (such as in detail in MN 111) because they are a natural development of concentration or quieting (refer to SN 36.10). I recommend reading MN 111.