Haj wouldn’t be completed without visiting aimma (or graves).

Ibn Babaweyh al-Qummi, shaykh of shias – as-Saduq in his “Ilal ush-Sharae” (2/450) narrated that Imam Jafar said:

 إذا حج أحدكم فليختم حجه بزيارتنا لان ذلك من تمام الحج .

If one of you would make a haj, let him finish his haj with our visitation, that is from completeness of haj.