Musnad Ahmad Hadith 15019

It is narrated from Jabir (may Allah be pleased with him) that once we were with the Prophet (peace and blessings of Allah be upon him) in the valley of Nakhlah. The Prophet (peace be upon him) led the companions in the Zuhr prayer. The polytheists intended to attack the Muslims and said, "Leave them; after this prayer, they will perform another prayer which is dearer to them than even their children." Jibreel came down and informed the Prophet (peace be upon him) about this. So, on this occasion, the Prophet (peace be upon him) divided us into two rows and stood at the front himself. The Prophet (peace be upon him) said the takbeer and we also said the takbeer with him. Then he bowed (in ruku‘) and we all bowed with him. Then, when he raised his head from ruku‘ and went into prostration (sajdah), only those in the first row performed sajdah with him, while the second row remained standing facing the enemy. When the Prophet (peace be upon him) and the people of the first row stood up, the people of the back row performed sajdah. After this, the people of the back row came forward and the people of the front row went to the back. Then we all bowed together, and when the Prophet (peace be upon him) performed sajdah, the people of the first row also performed sajdah, and when they sat down, the people of the back row also performed sajdah.