Hadith: We came with the Messenger of Allah (may Allah's peace and blessings be upon him) while we were pronouncing Talbiyah for Hajj, but the Messenger of Allah (may Allah's peace and blessings be upon him) commanded us; so we made it ‘Umrah

عن جابرٍ رضي الله عنه قال: قدِمنا مع رسولِ الله صلى الله عليه وسلم ، ونحنُ نقولُ: لبيك بالحجِّ، فأمرَنا رسولُ الله صلى الله عليه وسلم فجعلناها عُمرةً.
[صحيح] - [متفق عليه]

Jābir (may Allah be pleased with him) reported: We came with the Messenger of Allah (may Allah's peace and blessings be upon him) while we were pronouncing Talbiyah for Hajj, but the Messenger of Allah commanded us; so we made it ‘Umrah.'
[Authentic hadith] - [Narrated by Bukhari & Muslim]

Explanation

Jābir (may Allah be pleased with him) told that when they came with the Messenger of Allah to perform the Farewell Hajj, many of them only intended to perform Hajj. But Prophet told those who had not brought sacrificial animals with them to change their Hajj to ‘Umrah, so that they would perform ‘Umrah followed by Hajj. And they did so, may Allah be pleased with them.