Is it permissible to raise one's voice during the opening takbir in a silent prayer due to waswasah (whispers of the devil/obsessive thoughts)?

Raising one's voice with the takbīrat al-iḥrām (the opening takbīr) is prescribed for the imam in both silent and audible prayers, so that the congregants may hear him. As for the congregant (ma'mūm) and the one praying alone (munfarid), they should say the takbīrat al-iḥrām silently. If the one praying alone raises his voice, his prayer is valid, but the Sunnah is to say the takbīr silently. The cure for waswasah (whispers/obsessive thoughts) is to turn away from them and not pay attention to them. So, if Satan whispers to someone that his takbīr is not valid, one should not pay attention to his whispers.