Hajj and Umrah are both obligatory

It is narrated from Sayyiduna Zayd bin Thabit (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Indeed, Hajj and Umrah are two obligations; there is no harm to you whichever of them you begin with." And what is correct is that these are the words of Sayyiduna Zayd bin Thabit (may Allah be pleased with him) himself (mawquf).

It is narrated from Sayyiduna Muhammad bin Sirin (may Allah have mercy on him) that Sayyiduna Zayd bin Thabit (may Allah be pleased with him) was asked about performing Umrah before Hajj, and he said: They are like two prayers; it makes no difference to you whichever of them you begin with.

It is narrated from Sayyiduna Nafi' (may Allah have mercy on him) that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) used to say: Upon every one of Allah's creation who has the means, one Hajj and one Umrah are obligatory; then whatever one does after that is good and voluntary. Ibn Jurayj said: It reached me from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that he said: Umrah is obligatory just as Hajj is obligatory, provided one has the means.
This chain is sahih (authentic) on the condition of the two Shaykhs.