✅ Answer: Please refer to the following narrations:

1⃣عَنْ رَجُلٍ مِنْ أَصْحَابِنَا یُقَالُ لَهُ عَبْدُالرَّحْمَنِ بْنُ سِنَانٍ قَالَ: کُنْتُ عِنْدَ أَبِی عَبْداللَّهِ إِذْ دَخَلَ عَلَیْهِ رَجُلٌ فَأَعْطَاهُ ثَلَاثِینَ دِینَاراً یَحُجُّ بِهَا عَنْ إِسْمَاعِیلَ وَ لَمْ یَتْرُکْ شَیْئاً مِنَ الْعُمْرَةِ إِلَی الْحَجِّ إِلَّا اشْتَرَطَهُ عَلَیْهِ حَتَّی اشْتَرَطَ عَلَیْهِ أَنْ یَسْعَی عَنْ وَادِی مُحَسِّرٍ ثُمَّ قَالَ یَا هَذَا إِذَا أَنْتَ فَعَلْتَ هَذَا کَانَ لِإِسْمَاعِیلَ حَجَّةٌ بِمَا أَنْفَقَ مِنْ مَالِهِ و کَانَ لَکَ تِسْعٌ بِمَا أَتْعَبْتَ مِنْ بَدَنِک

📚 Al-Kafi, Vol. 4, p. 312

Abdulrahman said: I was with Imam Al-Sadiq (peace be upon him) when a man came to him. Imam gave him 30 dinars to perform Hajj on behalf of Isma'il and did not leave anything from the Umrah to Hajj except that he made a condition with him! He even made him agree to perform Sa'i in Wadi Muhassir!

Then he said: So-and-so, when you do this, Isma'il will have one Hajj due to spending from his wealth, and for you, there will be 9 Hajj due to the hardship you put your body through!

2⃣عن مُعَاوِیَةَ بْنِ عَمَّار عن أَبِی عَبْداللَّه قَالَ: إِذَا مَرَرْتَ بِوَادِی مُحَسِّرٍ وَ هُوَ وَادٍ عَظِیمٌ بَیْنَ جَمْعٍ و مِنًی و هُوَ إِلَی مِنًی أَقْرَبُ فَاسْعَ فِیهِ حَتَّی تُجَاوِزَهُ فَإِنَّ رَسُولَ اللَّه حَرَّکَ نَاقَتَهُ و قال اللَّهُمَّ سَلِّمْ لِی عَهْدِی و اقْبَلْ تَوْبَتِی و أَجِبْ دَعْوَتِی وَ اخْلُفْنِی فِیمَنْ تَرَکْتُ بَعْدِی

📚 Al-Kafi, Vol. 4, p. 470

Imam Al-Sadiq (peace be upon him) said: When you pass through Wadi Muhassir, which is a large valley between Muzdalifah and Mina, and closer to Mina, perform Sa'i (walk quickly) until you pass through it, because the Messenger of Allah (peace be upon him) made his camel move and said:

اللَّهُمَّ سَلِّمْ لِی عَهْدِی وَ اقْبَلْ تَوْبَتِی وَ أَجِبْ دَعْوَتِی وَ اخْلُفْنِی فِیمَنْ تَرَکْتُ بَعْدِی

3⃣عن عبدالْأَعْلَی عن أَبی عبداللَّه قال: إِذَا مَرَرْتَ بِوَادِی مُحَسِّرٍ فَاسْعَ فِیهِ فَإِنَّ رَسُولَ اللَّه سَعَی فِیه

📚 Al-Tahdheeb, Vol. 5, p. 195

Imam Al-Sadiq (peace be upon him) said: When you pass through Wadi Muhassir, perform Sa'i in it, because the Messenger of Allah (peace be upon him) did Sa'i in it!

4⃣عن حفص بن البختری و غیره عن أبی عبداللَّه أَنَّهُ قَالَ لِبَعْضِ وُلْدِهِ هَلْ سَعَیْتَ فِی وَادِی مُحَسِّرٍ فَقَالَ لَا قَالَ فَأَمَرَهُ أَنْ یَرْجِعَ حَتَّی یَسْعَی قَالَ فَقَالَ لَهُ ابْنُهُ لَا أَعْرِفُهُ فَقَالَ لَهُ سَلِ النَّاس

📚 Al-Kafi, Vol. 4, p. 470

Imam Al-Sadiq (peace be upon him) said to one of his children: Did you perform Sa'i in Wadi Muhassir? He said: No! Then the Imam commanded him to return and perform Sa'i there!

It is said: His son said to the Imam: I do not know it! So the Imam told him: Ask the people!

5⃣عن الحجال عن بعض أصحابنا قال: مَرَّ رَجُلٌ بِوَادِی مُحَسِّرٍ فَأَمَرَهُ أَبُو عَبْداللَّه بَعْدَ الِانْصِرَافِ إِلَی مَکَّةَ أَنْ یَرْجِعَ فَیَسْعَی

📚 Al-Kafi, Vol. 4, p. 470

One of the companions said: A man passed through Wadi Muhassir, and Imam Al-Sadiq (peace be upon him) commanded him to return to it and perform Sa'i after his return to Mecca!

6⃣و رَوَی مُحَمَّدُ بْنُ إِسْمَاعِیلَ عَنْ أَبِی الْحَسَنِ علیه السلام قال الْحَرَکَةُ فِی وَادِی مُحَسِّرٍ مِائَةُ خُطْوَةٍ

و فِی حَدِیثٍ آخَرَ مِائَةُ ذِرَاعٍ

📚 Al-Faqih, Vol. 2, p. 282

Imam Al-Kadhim (peace be upon him) said: The movement in Wadi Muhassir is equivalent to one hundred steps!

And in another narration, it is one hundred arms' length!

7⃣عن عُمَرَ بْنِ یَزِیدَ قال: الرَّمَلُ فِی وَادِی مُحَسِّرٍ قَدْرُ مِائَةِ ذِرَاعٍ

📚 Al-Kafi, Vol. 4, p. 471

Umar bin Yazid said: (The Imam) said: The brisk walk in Wadi Muhassir is equivalent to one hundred arms' length!

7⃣عن أبی بصیر عن أبی عَبْداللَّه قال: حَدُّ الْمُزْدَلِفَةِ مِنْ مُحَسِّرٍ إِلَی الْمَأْزِمَیْن

📚 Al-Kafi, Vol. 4, p. 471

Imam Al-Sadiq (peace be upon him) said: The boundary of Muzdalifah (Mish'ar) extends from Muhassir to Ma'zimayn!

✅ Based on the above narrations, Wadi Muhassir is an area located after the boundary of Muzdalifah, between Muzdalifah and Mina. It is emphasized in the above narrations that pilgrims, when traveling from Muzdalifah to Mina on the Day of Eid al-Adha, should perform Sa'i in it, either by walking briskly or with a quick pace, covering a distance of one hundred steps or one hundred arms' lengths. If someone neglects it, they should return and perform Sa'i for this distance.

The person riding should also make their mount move at this speed.

اللَّهُمَّ صَلِّ عَلَی مُحَمَّدٍ وَ آلِ مُحَمَّدٍ وَ عَجِّلْ لِوَلِیِّکَ الْفَرَجَ وَ الْعَافِیَةَ وَ النَّصْر