Tirmidhi

Explanation:
1:
In the narration of Sahih Bukhari, it is mentioned that the questioner had asked about the expiation (fidya) for killing a mosquito while in the state of ihram.
It is possible that in the author's narration, one of the narrators reported the narration ambiguously.
In terms of context and sequence, the correct situation regarding the issue is the one found in Sahih Bukhari.

Hadith Commentary:
To enumerate the virtues of these two flowers of the garden of Prophethood would require volumes; from the aforementioned ahadith, one can estimate their merits. The person who asked the question was a Kufan, and it was the people of Kufa who martyred Husayn (radi Allahu anhu).
From that very day, this saying became proverbial: "al-Kufi la yufi"—meaning, the people of Kufa are not loyal.

Hadith Commentary:
1.
In a narration of Jami‘ at-Tirmidhi, it is mentioned that the Messenger of Allah (sallallahu alayhi wa sallam) would call Hasan (radi Allahu anhu) and Husayn (radi Allahu anhu) to himself, smell them, and embrace them closely to his body.
(Fath al-Bari: 7/123)

2.
Abdullah ibn ‘Umar (radi Allahu anhu) expressed astonishment at a question, saying: “The people of Iraq are indeed strange! While in the state of ihram, they hesitate to kill a fly, considering it a violation for which a penalty must be paid.
Yet, with utmost shamelessness and brazenness, they martyred the grandson of the Messenger of Allah (sallallahu alayhi wa sallam), Husayn (radi Allahu anhu), and did not reflect in the least about what circumstances they would face on the Day of Resurrection for killing him, nor how they could hope for the intercession of the Messenger of Allah (sallallahu alayhi wa sallam).
One can only lament their understanding and intelligence: they inquire about the penalty and compensation for killing a trivial creature like a fly while, in the matter of killing the greatest of personalities, they acted with complete boldness and shamelessness.
Curse be upon the killers of Husayn, for they, in pursuit of worldly aims and base desires, mercilessly martyred the grandson of the Messenger of Allah (sallallahu alayhi wa sallam) and the beloved child of Sayyidah Fatimah (radi Allahu anha).
Inna lillahi wa inna ilayhi raji‘un.
“Bana kar dund khush rasme bakhak o khoon ghalatidan.”
...
May Allah have mercy upon these pure-hearted lovers.

Hadith Commentary:
Most of those who martyred Husayn (radi Allahu anhu) were residents of Kufa, who had repeatedly written letters inviting Husayn (radi Allahu anhu) to Kufa and assuring him of their loyalty. However, when the time came, all of them joined the enemies, and in the field of Karbala, everything transpired that the world knows. Truly, it is said:
Will the nation that killed Husayn (radi Allahu anhu) expect the intercession of his grandfather (sallallahu alayhi wa sallam) on the Day of Judgment?

Hadith Commentary:
(1)
Most of those who martyred Husayn (radi Allahu anhu) were the people of Kufa. They repeatedly wrote letters inviting him to Kufa and assured him of their loyalty, but when the time came, they all joined the enemies. Then, in the field of Karbala, what transpired is known to the world.

(2)
The relevance of this hadith to the chapter heading is as follows: The Messenger of Allah (sallallahu alayhi wa sallam) described Hasan and Husayn (radi Allahu anhuma) as two fragrant flowers, and a fragrant flower is smelled, and children are also smelled; while showing affection, they are kissed and embraced.

And Allah knows best.