ما حكم وضع الطرف العلوي للقدمين على الأرض أثناء السجود، وهل تكبيرة الهوي لسجود السهو القبلي والبعدي هي تكبيرة إحرام أم انتقال؟

Prostration on the seven limbs is required, and the majority of scholars consider it recommended, not obligatory. Prostrating on the tops of the feet does not invalidate the prayer. As for the takbir (saying "Allahu Akbar") during the prostration of forgetfulness (sujud as-sahw), there is a detailed explanation: regarding the sujud ba'di (prostration performed after the taslim), it has been said that one should intend it as the takbir of ihram (entering prayer) or of descending. As for the sujud qabli (prostration performed before the taslim), it is a takbir for descending.