Is my prayer valid if I say the opening Takbir (Takbirat al-Ihram) silently in an audible prayer?

It is sunnah (recommended) to vocalize the takbir and the recitation in a loud prayer, but it is not obligatory. Therefore, the prayer of one who whispers them is valid. For the utterance to be realized, it is necessary to move the tongue and articulate the letters. Jurists differed on whether the worshipper must hear themselves. The majority of jurists hold that this is obligatory, while the Malikis, some Hanafis, and Ibn Taymiyyah are of the opinion that merely moving the tongue and articulating the letters without sound is sufficient. This is the view preferred by Sheikh Ibn 'Uthaymeen. The preponderant view is that moving the tongue and lips with the takbir is sufficient, and it is better for it to be with a sound that one can hear.