The Prophet of Allah ﷺ uttered takbir and both rows uttered takbir together. Abu Dawud said: This tradition has been narrated by al-Thawri to the same effect on the authority of Khusaif. 'Abd al-Rahman b. Samurah also prayed in like manner. But the section which he (the Prophet) led in one rak'ah and then uttered the salutation and went and took the place of their companions. They came and prayed one rak'ah by themselves. Then they returned to their place and they prayed (one rak'ah) by themselves. Abu Dawud said: Muslim b. Ibrahim reported from 'Abd al-Samad b. Habib on the authority of his father that they had fought a battle at Kabul along with 'Abd al-Rahman b. Samurah. He led us in prayer in time of danger.  

فَكَبَّرَ نَبِيُّ اللَّهِ ﷺ وَكَبَّرَ الصَّفَّانِ جَمِيعًا