This excerpt is taken from Sheikh Farooq Rafi Sahib's book Qurbani, Aqiqa, and Ashra Zil-Hijjah.
The great sacrifice granted as ransom for Sayyiduna Ismail (peace be upon him) was a beautiful white ram with horns. The evidence for this is narrated from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) in the following hadith, which he reports:
ثم تله للجبين، وعلى إسماعيل قميص أبيض، فقال: يا أبت! إنه ليس لي ثوب تكفنني فيه غيره، فاخلعه حتى تكفنني فيه، فعالجه ليخلعه فنودي من خلفه، أن يا إبراهيم قد صدقت الرؤيا فالتفت إبراهيم، فإذا بكبش أبيض أقرن أعين، قال ابن عباس: لقد رأيتنا نبيع هذا الضرب من الكباش
"Then Sayyiduna Ibrahim (peace be upon him) laid Sayyiduna Ismail (peace be upon him) on one side of his face to slaughter him, and Sayyiduna Ismail was wearing a white shirt. He (Ismail) said: 'Father! I have no other cloth besides this shirt in which you can shroud me, so please remove it so that you can shroud me in it.' When he began to remove the shirt, a voice called from behind: 'O Ibrahim! You have indeed fulfilled the dream.' Then Sayyiduna Ibrahim (peace be upon him) looked back and suddenly there was a very beautiful white ram with horns. Sayyiduna Ibn Abbas (may Allah be pleased with him) says: 'Indeed, we used to buy such rams for sacrifice.'"
Reference: Sahih: Musnad Ahmad: 297/1, 2707. Sunan Bayhaqi: 154/5. Tarikh Dimashq: 210/6.
Benefits:
① Abu Asim Ghannawi is a trustworthy narrator; Yahya bin Ma'in has declared him trustworthy, so Abu Hatim's statement "لا أعرفه" does not detract from his trustworthiness.
Reference: (See Mizan al-I'tidal, Al-Jarh wa al-Ta'dil)
② Hammad bin Salamah is trustworthy and free from tadlis.
Reference: (See Fath al-Mubeen fi Tahqiq Tabaqat al-Mudallisīn by Zubair Ali Zai, p. 108. Therefore, the 'an'ana' of Hammad bin Salamah in Musnad Ahmad is not disparaging; moreover, in Tarikh Dimashq and Bayhaqi, there is no 'an'ana' but rather Hammad bin Salamah's hadith narration.)
Whether the sacrificed one (Dhabih) was Sayyiduna Ismail (peace be upon him) or Sayyiduna Ishaq (peace be upon him) is a matter of scholarly disagreement. Some scholars consider Sayyiduna Ishaq (peace be upon him) to be the sacrificed one, while others hold the opinion that the sacrificed one was Sayyiduna Ismail (peace be upon him). The latter opinion is more prevalent among scholars, and the evidence for it is as follows:
① After the determination to sacrifice Sayyiduna Ismail (peace be upon him) and the sacrifice of a sheep as his ransom, Allah Almighty gave glad tidings to Sayyiduna Ibrahim (peace be upon him) about the birth of Sayyiduna Ishaq (peace be upon him) and his prophethood. After this event of sacrifice, Allah Almighty gave this glad tiding:
﴿وَبَشَّرْنَاهُ بِإِسْحَاقَ نَبِيًّا مِّنَ الصَّالِحِينَ﴾
"And We gave him the good news of Isaac, a prophet from among the righteous."
Reference: Surah As-Saffat: 112
Similarly, with the birth of Sayyiduna Ishaq (peace be upon him), the glad tidings of the birth of Sayyiduna Yaqub (peace be upon him) were also given:
﴿فَبَشَّرْنَاهَا بِإِسْحَاقَ وَمِن وَرَاءِ إِسْحَاقَ يَعْقُوبَ﴾
"We gave her (i.e., Lady Sarah, may Allah be pleased with her) the glad tidings of Isaac and, after Isaac, Jacob."
Reference: Surah Hud: 71
So, the command of sacrifice seems pointless for the one whose birth was foretold along with prophethood and after whom the birth of his offspring Sayyiduna Yaqub (peace be upon him) was also announced. This would negate the previous glad tidings. On the contrary, the glad tidings given at the birth of Sayyiduna Ismail (peace be upon him) were:
﴿ فَبَشَّرْنَاهُ بِغُلَامٍ حَلِيمٍ﴾
"And We gave him the good news of a forbearing boy."
Reference: Surah As-Saffat: 101
Meaning, he would show great courage and extreme patience during a great calamity and severe trial, a character that Sayyiduna Ismail (peace be upon him) indeed demonstrated excellently. Therefore, the sacrificed one was Sayyiduna Ismail (peace be upon him).
② The command to sacrifice Sayyiduna Ismail (peace be upon him) was given to Sayyiduna Ibrahim (peace be upon him) in Makkah, and Sayyiduna Ishaq (peace be upon him) was not yet born at that time. Even after his birth, his childhood and youth were spent in the land of Sham (Syria). Whereas Sayyiduna Ismail (peace be upon him) resided in Makkah, and the command of sacrifice was revealed concerning him.
③ The following hadith from Musnad Ahmad resolves this dispute by clearly naming Sayyiduna Ismail (peace be upon him) as the sacrificed one, which is a clear text that the sacrificed one was indeed Sayyiduna Ismail (peace be upon him):
عرض له الشيطان عند المسعى، فسابقه فسبقه إبراهيم ثم ذهب به جبريل إلى جمرة العقبة، فعرض له الشيطان فرماه بسبع حصيات حتى ذهب، ثم عرض له عند الجمرة الوسطى، فرماه بسبع حصيات، ثم تله للجبين، وعلى إسماعيل قميص أبيض، فقال: يا أبت! إنه ليس لي ثوب تكفنني فيه غيره، فاخلعه حتى تكفنني فيه، فعالجه ليخلعه فنودي من خلفه، أن يا إبراهيم! قد صدقت الرؤيا فالتفت إبراهيم فإذا هو بكبش أبيض أقرن أعين
"When Sayyiduna Ibrahim (peace be upon him) was commanded to perform the rites of Hajj, near Maqam al-Sa’i, he encountered Satan, who tried to outrun him, but Sayyiduna Ibrahim (peace be upon him) overtook him. Then Sayyiduna Jibra’il (peace be upon him) took him towards Jamarat al-Aqaba, and when Satan appeared before him, he threw seven pebbles at him until he fled. Later, near Jamarat al-Wusta, he again encountered Satan and threw seven pebbles at him. At that place, Sayyiduna Ibrahim (peace be upon him) laid Sayyiduna Ismail (peace be upon him) on one side of his face, and Sayyiduna Ismail (peace be upon him) was wearing a white shirt. He said: 'Father! I have no other cloth except this shirt in which you can shroud me. Please remove it so that you can shroud me in it.' When he began to remove it, a voice came from behind: 'O Ibrahim! You have indeed fulfilled the dream.' Then Sayyiduna Ibrahim (peace be upon him) looked back and suddenly there was a white, beautiful ram with horns."
Reference: Sahih: Musnad Ahmad: 297/1. Sunan Bayhaqi: 154/5. Shu’ab al-Iman by Bayhaqi: 464/3. Tarikh Dimashq: 210/6.