Allama Hasan Shurunbulali (رحمة الله عليه) in his book “Maraqiul Falah, Sharh Nurul Ezah” has stated 18 wajib acts for salah in a comprehensive and brief way. According to most of the fuqha this number is authentic. However, if some books relate more or less than this number they are either the summary or explanation of these eighteen.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband