Hadith: When the Messenger of Allah (ﷺ) said: ''Sami‘allāhu liman hamidah (Allah hears whoever praises him),'' none of us would bend his back until the Prophet (ﷺ) had fallen in prostration. We would then fall in prostration right after him

عَنْ عَبْدِ اللَّهِ بْنِ يَزِيدَ الخَطْمِيِّ قَالَ: حَدَّثَنِي البَرَاءُ وَهُوَ غَيْرُ كَذُوبٍ، قَالَ:
كَانَ رَسُولُ اللَّهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ إِذَا قَالَ: سَمِعَ اللَّهُ لِمَنْ حَمِدَهُ، لَمْ يَحْنِ أَحَدٌ مِنَّا ظَهْرَهُ حَتَّى يَقَعَ النَّبِيُّ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ سَاجِدًا، ثُمَّ نَقَعُ سُجُودًا بَعْدَهُ.
[صحيح] - [متفق عليه] - [صحيح البخاري: 690]

‘Abdullah ibn Yazīd al-Khatmi reported: Al-Barā’—and he is not a liar—said to me:
When the Messenger of Allah (ﷺ) said: ''Sami‘allāhu liman hamidah (Allah hears whoever praises him),'' none of us would bend his back until the Prophet (ﷺ) had fallen in prostration. We would then fall in prostration right after him.
[Authentic hadith] - [Narrated by Bukhari & Muslim] - [Sahih Bukhari - 690]

Explanation

Al-Barā’ ibn ‘Āzib (may Allah be pleased with him) truthfully reported that when the Prophet (ﷺ) raised his head from bowing and said: Sami‘allāhu liman hamidah (Allah hears whoever praises Him), those behind him would remain standing, and none of them would bend his back to prostrate until the Prophet (ﷺ) had placed his forehead on the ground—then they would all prostrate after him.

Benefits from the Hadith

1. This describes how the Companions followed the Prophet (ﷺ) in prayer—they would not move from standing to prostration until he (ﷺ) had prostrated.
2. Ibn Daqīq al-‘Īd said: In this is evidence of the Prophet's (ﷺ) lengthy tranquility during prayer.
3. The conduct of the one led in prayer with the Imam has four states: 1. Musābaqah: It means preceding his Imam by performing a pillar before the Imam, for example, bowing or prostrating before the Imam does. This is forbidden. If one deliberately precedes the Imam knowing it is prohibited, his prayer becomes invalid—whether he performs a pillar before the Imam or reaches it before him. And if this happens in the opening Takbīr, the whole prayer is invalid, and he must repeat it from the beginning. 2. Muwāfaqah: This is when he performs actions of prayer at the same time as the Imam—bowing, prostrating, or rising with him. This is at least disliked, and based on apparent evidence, it is also prohibited. If one says the opening Takbīr simultaneously with the Imam, his whole prayer is invalid and must be repeated. 3. Mutāba‘ah: This means performing the acts of prayer after his Imam, without delay. This is the prescribed and Sunnah-compliant manner. 4. Takhalluf: This occurs when he delays so much from his Imam that it takes him out of proper following, such as when the Imam bows while the one praying behind him remains standing until the Imam is nearly rising from bowing. This is contrary to the prescribed manner and is prohibited, except when there is an excuse like illness or old age.