HIS/HER every dua is accepted for four months.

In a noble hadíth, Imam al-Bãqir (a.s.) said,

“Islam is based on five pillars: on prayer (salãt), alms (zakãt), pilgrimage (hajj), fasting (sawm), and devotion [to the Ahlul Bayt] (wilãya)." 1

Hadees 4: 

When a person completes a Hajj properly, his/her every dua is accepted for four months.

The Almighty has compared the negligence of hajj to ingratitude because of its importance. Hajj is one of the five pillars on which Islam is based.

When a person, on whom Hajj becomes wajib, completes the Hajj properly, his/her sins are forgiven such as if he/she is a newly born person.