Hanley opted off his country's Nation's Cup competition in Aachen amid speculation of horse doping, which arose after a German Equestrian official said they found a syringe in Hanley's jacket pocket at the CSI 3* in Balve from 11 to 14 June.
The horses were tested under the framework of the FEI Medication Control Programme (MCP) and returned negative results.
"The FEI has acted in consistence with its testing procedures and is satisfied with this result," said FEI General Counsel Lisa Lazarus.
"While the outcome of this situation establishes that none of Cameron Hanley's horses competing at Balve were administered prohibited substances, Mr Hanley acted appropriately by stepping aside from competition in Aachen to avoid attracting unnecessary attention to the Irish team.
"While it is never a positive thing to discover a used syringe on competition grounds - the decision to avoid competing to remove doubt as to the perceived fairness of competition should be commended."