1- It is Wajib (obligatory) on every free Mukallaf (person meeting the conditions to be held legally accountable for their actions i.e sane mind and able-body adult) Muslim, who is able, to perform Hajj and ‘Umrah once in a lifetime.

 2- It is wajib to perform Hajj straightaway if the person is able, according to the more correct of the two opinions maintained by scholars.

 3- Performing Hajj is wajib upon an indebted person who can pay off the debt and perform Hajj.

 4- It is better not to borrow money to perform Hajj.

 5- Anyone who abandons salaah (Prayer) or does not offer salaah regularly, their Hajj is not valid. The Prophet (peace be upon him) said: "The covenant that is between us and them (the hypocrites) is salaah. Anyone who abandons it has committed Kufr (disbelief)."  (Related by the Five Compilers of Hadith (Imams Ahmad, Abu Dawud, Al-Tirmidhi, Al-Nasa'ee and Ibn Majah) through an authentic Isnad [chain of narrators]) He (peace be upon him) also said: "Verily, between a person and Shirk (associating others with Allah in His Divinity or worship) and Kufr (disbelief) is the negligence of salaah. " (Related by Muslim in his Sahih [Authentic Hadith Book])

 6- Hajj performed with ill-gained money is valid because the rituals of Hajj are physical, however, a person must repent of having unlawful earnings.

 7- If a woman performs Hajj without a Mahram (spouse or unmarriageable relative), her Hajj is valid. However, she has sinned because it is not permissible for her to travel for Hajj, ‘Umrah or for any other purpose without a Mahram.

 8- It is permissible for a minor or a slave to perform Hajj, but it does not count as their obligatory Hajj. It was authentically reported by Ibn ‘Abbas (may Allah be pleased with them both) that the Prophet (peace be upon him) said: If a child performs Hajj, it will be obligatory for them to perform Hajj again when they attain puberty. Likewise, if a slave performs Hajj and then gets emancipated, they will have to perform Hajj again.  (Related by Ibn Abu Shaybah and Al-Bayhaqythrough good Isnad)

 9- Anyone who can afford Hajj but dies without performing it, their heirs should perform it on their behalf from the inheritance, whether the deceased requested it in their will or not.

 10- It is not valid to authorize someone to perform obligatory or supererogatory Hajj on behalf of a healthy person, even if they are poor. However, a person who is unable to perform Hajj due to old age or an incurable illness should charge someone to perform the obligatory Hajj and ‘Umrah on their behalf, if they can afford to pay for it themselves. Allah (Glorified be He) says: And Hajj (pilgrimage to Makkah) to the House (Ka‘bah) is a duty that mankind owes to Allâh, those who can afford the expenses (for one’s conveyance, provision and residence)

[Source:  A Guide to Hajj and Umrah by Shaykh Ibn Baaz]