Wasak wr wb,
In the Agile methodology, your project is divided into sprints. Depending on the phase of the project, different members of the team will participate in the project.
As a developer, I assume the Scrum Master would ask you what tasks you are comfortable to complete in the given time frame (Sprint - normally between 2-3 weeks). This would include not only your development tasks but also fixing of any bugs discovered by QA and tasks related to production support (if applicable).
If you are new to the agile environment, please understand that the first two sprints are commonly used to set the pace of the project. The managers will be able to gauge the accuracy of the estimates and the scrum master will calibrate the upcoming sprints accordingly.
If the Scrum Master or your manager, expects you to give an estimate of all the tasks for all future sprints or s/he asks you to underestimate the time taken to complete the tasks, then the sprint(s) will never have a full set of completed tasks. The fault does not lie with you since what you give is an 'estimate' as per the methodology.
With respect to the concept of 'Inshallah', most IT projects are conducted in a secular corporate environment. Hence, do not expect religious concepts to apply except when asking for a holiday on Christmas or Eid.