Tirmidhi

Explanation:
1:
That is, he will not be given any reward for this hardship.

2:
According to this hadith, if someone has made a vow (nazr) to walk to the Sacred House (Baytullah) on foot or barefoot, then fulfilling such a vow is neither necessary nor obligatory. And if a woman has vowed to go with her head uncovered, then she should not fulfill it at all, because this is an act of disobedience and sin.

Note:
(The narrator "Ubaydullah bin Zahr" is extremely weak. The part about fasting in this narration is weak, but there are authentic supporting narrations for the remaining portions.)

Hadith Commentary:
(1)
The name of the sister of Uqbah ibn Amir (radi Allahu anhu) mentioned in the hadith is Umm Hiban bint Amir, although her brother’s name is Uqbah ibn Amir ibn Nabi, who was an Ansari and participated in the Battle of Badr, and her husband’s name is Haram ibn Muhayyisa. There is no narration from this Uqbah in the books of hadith, whereas the Uqbah ibn Amir mentioned in the hadith refers to the one who belonged to the Juhaynah tribe, and there are several ahadith narrated from him in the books of hadith. He was neither an Ansari nor did he participate in the Battle of Badr, therefore the name of his sister could not be ascertained. She had made a vow (nadhar) that she would go to the House of Allah (Bayt Allah) without a head covering, on foot, and barefoot. Moreover, this woman was heavyset, weak, and unable to walk. Upon this, the Messenger of Allah (sallallahu alayhi wa sallam) said:
“She should cover her head, ride (an animal), and fast for three days as expiation (kaffarah) for her vow.”
(Sunan an-Nasa’i, Al-Ayman wa’n-Nudhur, Hadith: 3846)
In some narrations, she was ordered to slaughter a camel.
(Musnad Ahmad: 201/4)
Its details will be explained in the Book of Oaths and Vows (Kitab al-Ayman wa’n-Nudhur).
(Fath al-Bari: 103/4)
Insha’Allah.
(2)
Imam Bukhari (rahimahullah) has established at the end of the hadith that Abu’l-Khayr heard (sama‘) from Uqbah ibn Amir (radi Allahu anhu).

(1) There is no benefit in going on foot, and it is also possible to go on foot; therefore, this vow should be fulfilled, otherwise expiation (kaffarah) must be given. Although expiation is not mentioned in this narration, its affirmation is found in some other narrations, for example: 3846.

(2) "He should walk on foot and also ride"—one meaning is that he should walk as far as he is able, and when he becomes incapable, then he may ride. And it is possible that the intended meaning is that whether he walks or rides, but in the case of riding, expiation (kaffarah) will have to be given. Thus, due to such a vow being without benefit, it is not necessary to fulfill it; one may give expiation. According to the first meaning, it is necessary for him to walk as much as he is able. And Allah knows best.

(3) In the case of such a vow, from where should one start walking on foot? According to some jurists (fuqaha), one should start walking from one's home, and according to others, after donning the ihram at the miqat. The first meaning is more apparent, but at times it is not possible, for example: for those from Pakistan.

Takhrij:
«أخرجه البخاري، جزاء الصيد، باب من نذر المشي إلي الكعبة، حديث:1866، ومسلم، النذر، باب من نذرأن يمشي إلي الكعبة، حديث:1644، وحديث: "أن الله لا يصنع بشقاء أختك شيئًا" أخرجه أبوداود، الأيمان والنذور، حديث:3293، 3295، والترمذي، النذور والأيمان، حديث:1544، والنسائي، الأيمان والنذور، حديث:3845، وابن ماجه، الكفارات، حديث:2134، وأحمد:4 /145 وسنده ضعيف، عبيدالله بن زحر ضعيف، ضعفه الجمهور، وتابعه بكربن سوادة في رواية ابن لهيعة أخرجه أحمد:4 /147، وابن لهيعة ضعيف من جهة سوء حفظه.»©Explanation:
Our esteemed researcher has declared the last part of the narration «إِنَّ اللّٰہَ لاَ یَصْنَعُ بِشَقَآئِ …» to be weak in its chain of transmission, whereas other scholars have considered the rest of the narration, except for the phrase «وَلْتَصُمْ ثَلاَثَۃَ أَیَّامٍ», to be authentic. They have used the first part of the mentioned hadith as supporting evidence, in which there is no mention of fasting, and that narration is found in the two Sahihs (Sahih al-Bukhari and Sahih Muslim).
Therefore, the mentioned narration is authentic except for this phrase «وَلْتَصُمْ ثَلاَثَۃَ أَیَّامٍ» “and fast for three days.”
For further details, see: (Irwa’ al-Ghalil: 8/218, 221; and al-Mawsu‘ah al-Hadithiyyah, Musnad al-Imam Ahmad: 28/540, 542)