Tirmidhi

Explanation:
1:
From this, it is understood that it is permissible to engage in transactions such as taking a loan from the People of the Book (Ahl al-Kitab).
The Prophet (sallallahu alayhi wa sallam) took a loan from a Jew instead of taking it from any of the noble Companions (radi Allahu anhum) so that people would know that such dealings with the People of the Book are permissible.
Or it was because the Companions (radi Allahu anhum) did not like to take any compensation or payment back from the Prophet (sallallahu alayhi wa sallam), whereas the noble nature of the Prophet (sallallahu alayhi wa sallam) did not prefer this.

Hadith Commentary:
This hadith sheds light on the economic life of the Prophet sallallahu alayhi wa sallam.
God forbid, had he been worldly, the situation would not have arisen where he would have to pawn his armor with a Jew in order to obtain provisions—and even those provisions were in the form of barley. This clearly demonstrates that he presented an excellent example for those who would come after him: that in times of worldly luxury and indulgence, they should remember the example of Muhammad sallallahu alayhi wa sallam.
The purpose of this chapter is to show that sometimes in life, a person may have to purchase something on credit, and therefore there is nothing objectionable in this. It also establishes the permissibility of financial transactions with non-Muslims.

Hadith Commentary:
(1)
Imam Bukhari rahimahullah has restricted this chapter heading to the matter of the Messenger of Allah sallallahu alayhi wa sallam taking a loan, whereas in the Book of Loans (Kitab al-Istiqrad), he has mentioned it in an absolute sense. The purpose is to show that buying and selling on credit is permissible, and this is not a specific characteristic (khasais) of the Messenger of Allah sallallahu alayhi wa sallam.

(2)
In reality, Imam Bukhari rahimahullah intends to refute those individuals who consider transactions on credit to be impermissible. Their evidence is a hadith from Sunan Abi Dawud, in which the Messenger of Allah sallallahu alayhi wa sallam bought some goods on credit, and later said:
"In the future, I will only buy and sell when I have the price with me."
(Sunan Abi Dawud, al-Buyu', Hadith: 3344)
Imam Bukhari rahimahullah, through this chapter heading and the presented hadith, has indicated the weakness of that hadith, because the incident of purchasing from a Jew in exchange for a mortgaged coat of mail (dir‘) occurred in the last part of the life of the Messenger of Allah sallallahu alayhi wa sallam, to the extent that he was not able to pay the price and retrieve the mortgaged coat of mail.
In any case, conducting transactions on credit is permissible.

(3)
It should be noted that the Messenger of Allah sallallahu alayhi wa sallam conducted a loan transaction with a usurious Jew, but did not take a loan from any Muslim, because a Muslim, out of devotion, would have given it to him for free, whereas he sallallahu alayhi wa sallam did not like to accept anyone’s favor.
And Allah knows best.

Benefits and Issues:
The meaning of "sa‘" is a container that is used for measuring grain.
The sa‘ of the people of Madinah was approximately two and a half kilograms.