Allah Almighty has mentioned this event in Parah 26, Surah Az-Zariyaat, verses 24-30:

هَلْ اَتٰىكَ حَدِیْثُ ضَیْفِ اِبْرٰهِیْمَ الْمُكْرَمِیْنَۘ(۲۴) اِذْ دَخَلُوْا عَلَیْهِ فَقَالُوْا سَلٰمًاؕ-قَالَ سَلٰمٌۚ-قَوْمٌ مُّنْكَرُوْنَۚ(۲۵) فَرَاغَ اِلٰۤى اَهْلِهٖ فَجَآءَ بِعِجْلٍ سَمِیْنٍۙ(۲۶) فَقَرَّبَهٗۤ اِلَیْهِمْ قَالَ اَلَا تَاْكُلُوْنَ٘(۲۷) فَاَوْجَسَ مِنْهُمْ خِیْفَةًؕ-قَالُوْا لَا تَخَفْؕ-وَ بَشَّرُوْهُ بِغُلٰمٍ عَلِیْمٍ(۲۸) فَاَقْبَلَتِ امْرَاَتُهٗ فِیْ صَرَّةٍ فَصَكَّتْ وَجْهَهَا وَ قَالَتْ عَجُوْزٌ عَقِیْمٌ(۲۹) قَالُوْا كَذٰلِكِۙ-قَالَ رَبُّكِؕ-اِنَّهٗ هُوَ الْحَكِیْمُ الْعَلِیْمُ(۳۰)

Did the news of Ibrahim’s honourable guests reach you (O Beloved)? When they came to him (and) said, ‘Salaam.’ He (also) answered, ‘Salaam.’ (And said) ‘These people are strangers.’ Then he went to his home, so he brought a healthy (roasted) calf. He then presented it before them, (and) said, ‘Do you not eat?’ So, he inwardly began fearing them. They said, ‘Do not fear.’ And they gave him the glad tidings of a knowledgeable son. His wife came screaming, then struck her forehead and said, ‘What! An old infertile woman (will give birth to a child)?’ They said (to the wife of Ibrahim), ‘This is how your Lord has commanded. Indeed, only He is the Wise, the All-Knowing.’

[Kanz-ul-Iman (translation of Quran)] (Part 26, Surah Al-Zariyaat, Verses 24-30)

Shaykh-ul-Hadith, ‘Allamah ‘Abdul Mustafa A’zami رَحْمَةُ الـلّٰـهِ عَلَيْه states regarding the aforementioned event: From this event we learn that angels sometimes come in the form of humans to people. It is mentioned in a few narrations: on the occasion of Hajj, some groups of angels appear in the form of humans at the Ka’bah, Mina, ‘Arafat, Muzdalifah, etc. and they are sent towards the pilgrims to test them.

Therefore, it is necessary for the honourable pilgrims to remain aware at Makkah, Mina, ‘Arafat, Muzdalifah, circumambulation of Ka’bah and