What is the ruling on secretly saying "Allahu Akbar" when prostrating after Qunut, or prostrating without it?

The Imam's audible declaration of the Takbir (Allahu Akbar) is recommended. The prayer is not invalidated by intentionally omitting it, nor is the prostration of forgetfulness (sujud as-sahw) required if it is unintentionally omitted, according to the majority of scholars.

The ruling on the Takbirat al-Intiqal (Takbir of transition between prayer postures) differs: The majority of jurists consider it recommended, so the prayer is not invalidated by intentionally or unintentionally omitting it. In contrast, the Hanbalis consider it obligatory, stating that the prayer is invalidated by intentionally omitting it, and the prostration of forgetfulness is required for unintentional omission. The Malikis consider it recommended, and the prostration of forgetfulness is required if two Takbirat are unintentionally omitted.