When the Prophet ﷺ wanted to prostrate after bowing, he would say: "Allahumma, Rabbana wa lakal-hamd, mil'as-samawati wa mil'al-ardi wa mil'ama shi'ta min shai'in ba'd ( O Allah, our Lord, to You be the Praise, filling the heavens, filling the Earth, and filling whatever else You will.)"
أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا أَرَادَ السُّجُودَ بَعْدَ الرَّكْعَةِ يَقُولُ اللَّهُمَّ رَبَّنَا وَلَكَ الْحَمْدُ مِلْءَ السَّمَوَاتِ وَمِلْءَ الأَرْضِ وَمِلْءَ مَا شِئْتَ مِنْ شَىْءٍ بَعْدُ