Day of Judgement heard this. Those who were fortunate responded with لَبَّیْک.^[1]

Imam Mujāhid رَحْمَةُ الـلّٰـهِ عَلَيْه elucidates:

Those who responded with لَبَّیْک will perform ḥajj in their lives. Whoever responded once shall perform ḥajj once, whoever responded twice shall perform it twice, and whoever responded numerous times shall perform it numerous times.^[2]

سُـبْحٰـنَ الـلّٰــه Dear Islamic brothers! Anyone who undertakes ḥajj today, spends money for it, remains patient upon any difficulties they encounter in its process, makes ṭawāf of the Kaʿbah, takes up sojourn in Mīnā, Muzdalifah and the plains of ʿArafah, and runs between Ṣafā and Marwah; this is all evidence that these fortunate people said لَبَّیْک in response to the call of Prophet Ibrāhīm عَلَیْہِ السَّلَام.

Who is ḥajj obligatory upon?

O those who love Allah’s Messenger! Ḥajj is obligatory upon every Muslim possessing means to perform it. Allah declared in His Quran:  

وَ لِلہِ عَلَی النَّاسِ حِجُّ الۡبَیۡتِ مَنِ اسۡتَطَاعَ اِلَیۡہِ سَبِیۡلًا ؕ

And performing ḥajj of this House, for the sake of Allah, is (an obligation) upon the people, who have the means to reach it.^[3]

We thus learn that ḥajj is obligatory upon whoever possesses means to reach the Kaʿbah. The beloved Prophet صَلَّى الـلّٰـهُ عَلَيْهِ وَاٰلِهٖ وَسَلَّم explained how these means refers to mode of transport and travel expenses.