Hadith 721

وَقَالَ : وَلَوْ يَعْلَمُونَ مَا فِي التَّهْجِيرِ لَاسْتَبَقُوا ، وَلَوْ يَعْلَمُونَ مَا فِي الْعَتَمَةِ وَالصُّبْحِ لَأَتَوْهُمَا وَلَوْ حَبْوًا ، وَلَوْ يَعْلَمُونَ مَا فِي الصَّفِّ الْمُقَدَّمِ لَاسْتَهَمُوا " .
And then he added, "If the people knew the Reward for the Zuhr prayer in its early time, they would race for it. If they knew the reward for the `Isha' and the Fajr prayers in congregation, they would join them even if they had to crawl. If they knew the reward for the first row, they would draw lots for it."
Hadith Reference صحيح البخاري / كتاب الأذان / 721
Hadith Grading محدثین: أحاديث صحيح البخاريّ كلّها صحيحة
Explanation & Benefits
Maulana Dawood Raz
Hadith Commentary:
If, by coincidence, any Muslim man or woman drowns in water and dies, or falls victim to diseases of the stomach such as cholera, or passes away due to the plague, or dies by being crushed under a wall or something similar, all such individuals have been counted among those who receive the ruling of martyrs (shuhada).

By "the first row," what is meant is the row closest to the imam.

Qastallani rahimahullah has said that the "front row" also includes the second row, because it is ahead of the third row; in the same way, the third row is included because it is ahead of the fourth.

This hadith has already been mentioned previously.
Source: Sahih Bukhari: Commentary by Maulana Dawood Raz, Page: 721
Shaykh Abdul Sattar al-Hammad
Hadith Commentary:
(1)
There is a difference of opinion among the early scholars regarding who is included in the meaning of the "first row" (saff awwal). Some people are of the view that those who enter the mosque first are included in the first row, regardless of where they stand. Imam Bukhari rahimahullah states that those meant by "the people of the first row" are those who are directly adjacent to the imam, meaning that there is no one between them and the imam except the imam himself, because the wording in the hadith is (al-saff al-muqaddam). In view of these very words, Imam Bukhari rahimahullah has established the chapter heading "The First Row." If what was meant was those who enter the mosque first, then what would be the need for drawing lots? (Fath al-Bari: 2/270)

(2)
If a person is in the first row, and then his teacher or a respected elder arrives, and he steps back himself to give him a place in the first row, is this permissible? Some scholars say that this kind of self-sacrifice (ithar) is not permissible. However, there is detail in this matter: if the person sitting in the first row gives up his place for someone who is worldly, wealthy, or affluent, then it is not permissible. However, if he shows self-sacrifice for someone who is religious, and habitually prays in the first row but was delayed due to some excuse, then in such a case, self-sacrifice is permissible. Perhaps the reward for this self-sacrifice may even exceed the reward of being in the first row. In short, in this matter, worldly status or wealth should not be taken into consideration. And Allah knows best.
Source: Hidayat al-Qari: Commentary on Sahih Bukhari, Urdu, Page: 721