This is a sound hadith.

837 — ʿAbd ibn Ḥumayd narrated to us, saying: Yaʿqūb ibn Ibrāhīm ibn Saʿd informed me, saying: My father narrated to us, from Ṣāliḥ ibn Kaysān, from Ibn Shihāb, that Sālim ibn ʿAbd Allāh narrated to him

that he heard a man from the people of Syria asking ʿAbd Allāh ibn ʿUmar about tamattuʿ (performing ʿumrah before ḥajj), and ʿAbd Allāh ibn ʿUmar said: "It is lawful." The Syrian said: "But your father forbade it." ʿAbd Allāh ibn ʿUmar said: "What do you think—if my father forbade it, while the Messenger of Allah, peace and blessings be upon him, did it, is my father's command to be followed, or the command of the Messenger of Allah, peace and blessings be upon him?" The man said: "Rather, the command of the Messenger of Allah, peace and blessings be upon him." He said: "Indeed, the Messenger of Allah, peace and blessings be upon him, did it."

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= His saying: "And this one, on that day, was a disbeliever at al-ʿUrush"—the reference in "this" is to Muʿāwiyah ibn Abī Sufyān, and the meaning is: we performed tamattuʿ while Muʿāwiyah on that day was a disbeliever following the religion of the pre-Islamic era, residing in Mecca. See Sharḥ Muslim 8/204.

(1) In (A) and (D), and the copy upon which al-Ḥāfiẓ al-ʿIrāqī wrote his commentary, it appears as "ḥasan ṣaḥīḥ" (good and sound); the wording given is from the remaining manuscript sources.

(2) Sound. Aḥmad (5700) recorded it, and al-Nasāʾī recorded it in al-Kubrā (4229) via the chain of Maʿmar, from al-Zuhrī, with the wording: "ʿUmrah during the months of ḥajj is complete; the Messenger of Allah, peace and blessings be upon him, practiced it, and Allah revealed it in His Book."
Al-Bukhārī (1774) and Abū Dāwūd (1986) recorded it via the chain of Ibn Jurayj, that ʿIkrimah ibn Khālid asked Ibn ʿUmar, may Allah be pleased with them both, about ʿumrah before ḥajj, and he said: "There is no harm in it." ʿIkrimah said: Ibn ʿUmar said: "The Prophet, peace and blessings be upon him, performed ʿumrah before performing ḥajj."