يستحب لمن لقي الحاج ان يدعو له قائلا : تقبل الله طاعتكم وان يطلب منه ان يستغفر الله له ، فيرد الحاج مثلا : غفر الله لنا ولكم. قال رسول الله صلى الله عليه وسلم : اللهم اغفر للحاج ولمن استغفر له الحاج . رواه البيهقي .

Our beloved Prophet Sallallahu ^alayhi wa sallam made a supplication to Allah to forgive the sins of the person who has performed hajj. The Prophet also asked Allah to forgive the sins of the one whom a similar supplication has been made for by the person who performed hajj.

So when you meet a person who has perfomed hajj, it is highly recommeded to say to him / her : may Allah accept your acts of worship ( taqabballahu taa^atakum) then to request from them to ask Allah's forgivness for you.

May Allah forgive all our sins, Ameen