Tirmidhi

Hadith Commentary:
Hafiz Ibn Hajar rahimahullah has mentioned the background of this hadith with reference to Tabarani, stating that the narrator of the hadith, Abdullah bin Yazid, used to lead the people in prayer in Kufa. Upon this, he narrated this hadith as a refutation of their aforementioned action. (Fath al-Bari: 2/236)

In this hadith, the following of the imam is described. Accordingly, Imam Abu Dawud rahimahullah has established a chapter in his Sunan with the following words: “The follower should completely follow the imam.” Under this, he has brought a hadith of Muawiyah bin Abu Sufyan radi Allahu anhu that the Messenger of Allah sallallahu alayhi wa sallam said: “Do not go ahead of me in bowing (ruku‘) and prostration (sujud); whatever amount I perform bowing (or prostration) before you, you will attain that when I raise my head before you, because I have become heavy.” (Sunan Abi Dawud, al-Salat, Hadith: 619)

That is, when I raise my head from bowing or prostration, you will still be in bowing and prostration; this will be compensation for the delay that occurred because you went into bowing or prostration after me.

When the body of the Messenger of Allah sallallahu alayhi wa sallam became heavy, he gave special instruction to his noble companions radi Allahu anhum that, due to their habitual following, they should not fall into the error of competing or hastening ahead.

From this, the clear negation of simultaneity (muqaranah) is established.

This means that the followers should keep their eyes on the actions of their imam; when he becomes engaged in a pillar (rukn), then they are permitted to become engaged in that pillar. Before that, or simultaneously with him, or after he has completed the pillar, they are not permitted to become engaged in it. (Fath al-Bari: 2/236)

Hadith Commentary:

In essence, placing the forehead on the ground is what constitutes prostration (sujud), and the nose is included as part of the forehead. Therefore, it is obligatory (wajib) to place both the nose and the forehead on the ground. Then, placing both hands and both knees on the ground, and turning the toes of both feet towards the qiblah—these make a total of seven limbs upon which prostration is performed.

Hadith Commentary:
(1)
It is prohibited for the follower (muqtadi) to engage in any pillar (rukn) of the prayer before the imam, and for this reason, the noble Companions (radi Allahu anhum) were extremely mindful of this prohibitive ruling.

(2)
Allamah Kirmani (rahimahullah) has explained the relevance of this hadith to the chapter heading in these words: Generally, during prostration (sujud), the forehead is placed on the ground with the assistance of the other six limbs. Since in this hadith the other limbs of prostration are not mentioned, therefore, in those narrations where only the forehead is mentioned, it is due to the forehead being the most noble of the limbs of prostration compared to the others.

Some have also said that prostrating on the forehead is obligatory (wajib), which is why in some narrations only the forehead is mentioned, and prostration on the remaining limbs is recommended (mustahabb), so in some narrations they have been omitted.

(Fath al-Bari: 2/384)

However, this position is not correct, because prostrating on seven limbs has been expressed with the wording of command (amr), which indicates obligation (wujub). Therefore, it is not correct to suffice with some limbs while leaving out others.

Yes, if there is a valid excuse preventing it, then that is a different matter.

Hadith Commentary: Benefits and Issues: The statement of Abdullah bin Yazid regarding al-Bara’ radi Allahu anhu, describing him as “not a liar,” even though, according to the principle that all the Companions (al-sahabah) are upright (‘udul), there is no need for this; it is merely for his praise and commendation, not for authentication or emphasis. And from this hadith, it is established that the follower (muqtadi) should not bow down for prostration (sujud) until the imam has placed his forehead on the ground.

830. Commentary: It is possible that the imam is elderly or has some ailment due to which it takes him longer to reach the position of prostration (sajdah). If the followers (muqtadis) begin to go into prostration as soon as the imam bows his head, then it is possible that those followers who are swift or young may reach the prostration before the imam. Therefore, it is necessary that the followers should only bend for prostration when the imam has placed his head on the ground in prostration. Similarly, when standing up for the next rak‘ah, one should wait until the imam is fully standing upright, and then the followers should begin to rise, so that there remains no possibility of preceding the imam.