Al-Khattābī said in Maʿālim al-Sunan (4/358) while commenting on the ḥadīth:

“This censure appears to stem from the fact that one has only been commanded to swear by Allah and by His attributes. The trust (al-amānah) is not one of His attributes; rather, it is one of His ordinances and a duty He has prescribed. They were therefore forbidden to swear by it, for doing so would equate it with the names and attributes of Allah.”

95 – “Look at her, for there is something about the eyes of the Anṣār”—meaning that they are small.

It was recorded by Muslim in his Ṣaḥīḥ (4/142), by Saʿīd ibn Manṣūr in his Sunan (523), and likewise by al-Nasāʾī (2/73), al-Ṭaḥāwī in Sharḥ al-Maʿānī (2/8), al-Dāraqutnī (396), and al-Bayhaqī (7/84) through Abū Ḥāzim, from Abū Hurayrah:

“A man wished to marry a woman from among the Anṣār, so the Messenger of Allah ﷺ said …”

I say: and he proceeded to mention it. The wording given here is that of al-Ṭaḥāwī, whereas the version preserved by Muslim and al-Bayhaqī states:

“I was with the Prophet ﷺ when a man came and told him that he had married a woman from the Anṣār, whereupon he said to him …”