Bukhari

Hadith Commentary:
From all these ahadith, the Imam (rahimahullah) has established the obligation of fulfilling promises, especially those promises made in a court of law; if one does not fulfill such a promise, then it will be enforced by compulsion.
Otherwise, the court would become a spectacle.
In front of Musa (alayhis salam), two periods were set: eight and ten years.
Shu’ayb (alayhis salam) had said to him that he wished to marry one of his two daughters to him, on the condition that Musa (alayhis salam) serve him for eight years, and if he completed ten years, then that would be a favor from him.
The meaning of the last sentence of the hadith is that the Messenger of Allah (sallallahu alayhi wa sallam) could never break a promise.
From here, the translation of the chapter heading is derived.
In another narration, it is stated that Sa’id said: Then that Jew met me, so I informed him of what Ibn Abbas (radi Allahu anhu) had said.
He replied, “Indeed, Ibn Abbas (radi Allahu anhu) is knowledgeable.”
Ibn Abbas (radi Allahu anhu) had heard this from the Prophet (sallallahu alayhi wa sallam), and he had asked Jibril (alayhis salam) about it.
Jibril (alayhis salam) had asked Allah the Exalted, in response to which Allah the Exalted said that Musa (alayhis salam) fulfilled the period which was longer and better.

Hadith Commentary:
(1)
From these ahadith, Imam Bukhari rahimahullah has established the obligation of fulfilling promises, especially those promises that are made in the presence of a court. If one does not fulfill such a promise, then the court should take notice of it and enforce its fulfillment by compulsion; otherwise, judicial decisions would become a mockery.

(2)
Two periods were set before Musa alayhis salam: eight years and ten years. Musa alayhis salam fulfilled the period that was longer and better, even though Musa alayhis salam had not promised ten years, yet he still fulfilled it. From this, the emphasis on fulfilling promises is intended. The meaning of the last sentence of this hadith is that whoever is a Messenger of Allah, he speaks the truth. His promise is true, and he does not violate it. The Messengers of Allah never break their promises. And Allah knows best.

Benefit:
Every single person's lifespan is predetermined; not even a moment can be advanced or delayed—this is our belief. Sayyiduna Musa (alayhis salam) was given the choice between life and death, and after discussion and deliberation, he agreed to have his death occur near Masjid al-Aqsa. This matter is mentioned in this hadith: that death came to him when his lifespan was complete and perfect, and it came at the appointed time—neither before nor after.