Tirmidhi

1:
The purpose of this admonition is that the fasting person should protect himself from every kind of sin while in the state of fasting, so that he may become deserving of the reward of fasting. This absolutely does not mean that he should start eating and drinking during Ramadan.

Hadith Commentary:
That is, if one does not abstain from lying, deceit, and evil deeds, then the fast will be nothing more than mere hunger; Allah has no need for our hunger. He knows that by fasting, we should abstain from evil words and bad habits, and bring our carnal desires under the control of sound reason and the straight path of Shari‘ah.

Hadith Commentary:
(1)
After beginning the fast, one should abstain from false speech and bad habits; in addition, one’s carnal desires should also be subjected to the Islamic Shariah. Whoever, after beginning the fast, does not abandon lying, deceit, and evil speech, then he has no fast—instead, he is merely enduring hunger for no reason.
Allah Ta’ala has no need for such self-imposed hunger.
(2)
In any case, after beginning the fast, one should fulfill its rights and etiquettes; otherwise, such a fast is deprived of acceptance in the court of Allah Ta’ala.
Hafiz Ibn Hajar rahimahullah writes that backbiting is a major sin, and the sin incurred by committing it greatly diminishes the reward of the fast—indeed, at times, nothing remains at all, as if that fast is considered as having been broken.
(Fath al-Bari: 10/582)

Hadith Commentary:
It is understood from this that a person who does not abstain from lying and deceit while fasting is disrespecting the fast; therefore, his fast holds no weight in the sight of Allah. Al-Baydawi said: “The purpose of the legislation of fasting is not merely hunger and thirst, but rather what follows from it—breaking the desires and subjugating the commanding soul (nafs al-ammara) to the tranquil soul (nafs al-mutma’inna). If this is not achieved, Allah does not look at such a fast with acceptance.”
(: Fath)

That is, the mere hunger and thirst are not intended from fasting; rather, the intention is also to abandon carnal desires, to incline the commanding soul (nafs al-ammara) towards obedience so that it may follow the tranquil soul (nafs al-mutma’inna).
If these objectives are not achieved, then Allah, the Exalted, will not look upon such a fast with acceptance.

The odor from the mouth of the fasting person is more beloved to Allah than musk.

Regarding this, Shah Waliullah Muhaddith Dehlawi rahimahullah states that, in his view, the reason for this is that when an act of worship is beloved, its effect also becomes beloved, and in the world of similitudes (alam al-mithal), that effect is manifested in place of the act of worship itself. For this reason, the Prophet sallallahu alayhi wa sallam placed, on one side, the joy that the angels experience and Allah’s pleasure due to this cause, and on the other side, the delight that the children of Adam feel from smelling musk, so that this hidden secret may become apparent to them.
(: Hujjat Allah al-Baligha)

Hadith Commentary:
(1)
The purpose of fasting is that a person becomes pious and adopts taqwa (God-consciousness). If this purpose is not achieved, then it is not fasting but mere starvation, for which Allah has no need, because the fasting person, through lying and deceit, dishonors the fast. Hafiz Ibn Hajar rahimahullah, quoting Qadi Baydawi rahimahullah, writes that the purpose of fasting is not merely to remain hungry and thirsty, but rather its aim is to eliminate carnal desires and to make the commanding soul (nafs ammara) subservient to the contented soul (nafs mutma'inna). When the fasting person does not attain these things, then Allah ta'ala will not look upon him with mercy, nor will He bestow the honor of acceptance upon such a fast. This does not mean that the one who lies should be ordered to abandon the fast; rather, the purpose is to restrain the fasting person from such evil actions. (Fath al-Bari: 151/4) And Allah knows best.

(2)
By "qawl az-zur" is meant lying; slander and acting upon falsehood are also included in this, and likewise, not refraining from those things which Allah ta'ala has forbidden is to act upon falsehood.

(3)
Imam Bukhari rahimahullah did not mention the apodosis (jawab al-shart) in his chapter heading because its clarification was present in the hadith itself. Furthermore, if he had mentioned it, the heading would have become quite lengthy, so Imam Bukhari, as per his usual practice, omitted it. (Umdat al-Qari: 33/8)

Benefits and Issues:
Allah Ta’ala has no need for any action of the children of Adam.
It is only due to His own wisdom and requirement that He has made them bound to the Shari’ah matters.
From this hadith, it is understood that a person should keep himself away from all motives in all his speech and actions.
He should not backbite, should not lie, should not slander, should not sell unlawful (haram) things. When a person stays away from these things for the entire month, then it is hoped that his soul will, by the grace and mercy of Allah, remain protected from these things in the remaining months of the year as well.
But it is extremely regrettable that many who fast do not differentiate between Ramadan and other months; the same lying, vain talk, deceit, etc., continue as per their habit.
Ramadan has no effect upon them.
Undoubtedly, the actions mentioned in the hadith do not break the fast, but they certainly reduce its reward, and it is also possible that if one is excessively heedless of these actions, the reward of the fast itself may be lost.

Benefits and Issues:

➊
The fundamental purpose of fasting is the attainment of taqwa (piety), as Allah the Exalted has said:
﴿يَـٰٓأَيُّهَا ٱلَّذِينَ ءَامَنُوا۟ كُتِبَ عَلَيْكُمُ ٱلصِّيَامُ كَمَا كُتِبَ عَلَى ٱلَّذِينَ مِن قَبْلِكُمْ لَعَلَّكُمْ تَتَّقُونَ﴾ ()
“O you who believe! Fasting has been prescribed for you as it was prescribed for those before you, so that you may become pious.”

➋
For the attainment of taqwa, merely abstaining from food and drink is not sufficient; rather, a conscious effort to avoid all kinds of sins is required. By fasting, we abstain from things made lawful (halal) by Allah, in accordance with His command. Therefore, it is even more necessary to avoid those acts that were already prohibited, so that the believer becomes accustomed to abstaining from them.

➌
In Islamic law (Shari‘ah), speaking during fasting is permissible. In fact, a fast of silence is legislatively prohibited. See: (Sahih al-Bukhari, Book of Faith and Vows, Chapter: Vows concerning what one does not possess and in disobedience, Hadith: 6704)

➍
Acts of worship have been prescribed for the spiritual and physical benefit of mankind. It is from the mercy of Allah that He bestows great rewards in the Hereafter for these deeds as well.

Lexical Explanation 538:
Lam yada‘: did not leave, did not abandon. Yada‘ is derived from wada‘.
Al-zur: the “za” has a dammah and the “waw” is sakin, meaning lying and vain speech.
Al-jahl: foolishness, stupidity, and harshness.
Fa laysa lillahi hajah: then Allah has no need for it, i.e., Allah has no attention or need for it. This means that such a deed is not acceptable to Allah.

Benefits and Issues 538:
➊ From this hadith, it is understood that in the state of fasting, one should abandon lying, false statements, and acts of ignorance and foolishness. The spirit of fasting cannot remain unaffected by lying and falsehood; therefore, it is extremely necessary for the fasting person to avoid these actions while fasting.
➋ Along with the physical training of the fasting person, there is also spiritual training. In other words, the purpose of fasting is that a person learns to control his temperament. He should avoid lying, deceit, fraud, and acts of ignorance. If this objective is not achieved, then there is no benefit in keeping the fast.