Does the integrated management system require a manual. Is it mandatory? If so, which clause it state?

Integrated system means a common QHSE system which covers all the requirements of the three standards i.e. ISO 9001, ISO 14001 and OHSAS 18001. It is not categorically mention anywhere in the standards that there should be a manual. But it is always a good decision to draft manual and have various procedures , sample forms , SOPs etc in the manual . It makes your life easy to comply with the requirements of the standards.

Any management system, either separated or integrated need manual, because it shows how to apply the system in the organization