Abdullah bin Abbas reported,

The Prophet ﷺ stood to pray, and the people stood with him. He pronounced the takbir and they pronounced it with him. He bowed, and some of them bowed with him. Then he prostrated, and they prostrated with him. When he rose for the second unit, those who had prostrated with him stood up and kept watch for their brothers, while the other group came forward and bowed and prostrated with him. All the people were in prayer, but they were guarding one another.

Azami 2916

Sahih

عن ابن عباس قال

قام النبي ﷺ، وقام الناس معه فكبر وكبروا معه، وركع وركع ناس منهم، ثم سجد وسجدوا معه، ثم قام للثانية فقام الذين سجدوا وحرسوا لإخوانهم، وأنت الطائفة الأخرى فركعوا وسجدوا معه، والناس كلهم في صلاة، ولكن يحرس بعضهم بعضا.

الأعظمي 2916صحيح
Contents
Reference
Commentary
Ayat
Collection
Jami al-Kamil
Book
Prayer
Chapter
Prayer of fear
Section
Guarding one another during the fear prayer
Numbering
Jami al-Kamil 2916 (2nd edition)
Azami 2916