Itmam At-Takbir (i.e., to end the number of Takbir, or to say the Takbir perfectly) on prostrating. [See Fath Al-Bari]
حَدَّثَنَا أَبُو النُّعْمَانِ، قَالَ حَدَّثَنَا حَمَّادٌ، عَنْ غَيْلاَنَ بْنِ جَرِيرٍ، عَنْ مُطَرِّفِ بْنِ عَبْدِ اللَّهِ، قَالَ صَلَّيْتُ خَلْفَ عَلِيِّ بْنِ أَبِي طَالِبٍ ـ رضى الله عنه ـ أَنَا وَعِمْرَانُ بْنُ حُصَيْنٍ،، فَكَانَ إِذَا سَجَدَ كَبَّرَ، وَإِذَا رَفَعَ رَأْسَهُ كَبَّرَ، وَإِذَا نَهَضَ مِنَ الرَّكْعَتَيْنِ كَبَّرَ، فَلَمَّا قَضَى الصَّلاَةَ أَخَذَ بِيَدِي عِمْرَانُ بْنُ حُصَيْنٍ فَقَالَ قَدْ ذَكَّرَنِي هَذَا صَلاَةَ مُحَمَّدٍ صلى الله عليه وسلم. أَوْ قَالَ لَقَدْ صَلَّى بِنَا صَلاَةَ مُحَمَّدٍ صلى الله عليه وسلم.
Narrated Mutarrif bin `Abdullah: `Imran bin Husain and I offered the prayer behind `Ali bin Abi Talib. When `Ali prostrated, he said the Takbir, when he raised his head, he said the Takbir and when he got up for the third rak`a he said the Takbir. On completion of the prayer `Imran took my hand and said, "This (i.e. `Ali) made me remember the prayer of Muhammad" Or he said, "He led us in a prayer like that of Muhammad."