In general, it is not common practice for a company to prevent an employee from submitting a resignation letter during their bond period. Employees typically have the right to resign at any time, although they may be required to serve out the notice period specified in their contract. It is possible that the 'no resignation during bond period' policy is specific to this company, but it is not a standard practice in most organizations. It is important for your colleague to review their employment contract and seek clarification from HR to better understand the company's policies and their rights as an employee.