This action towards Imam (aj) which is the best action of people proves that proxy Ziarat is Mustahab, and other factors also prove it.
1. For example the proof that giving Sadaqah on his behalf is Mustahab.
2. The reason for the Istehab of proxy Hajj and Tawaf also proves that proxy Ziarat is Mustahab.
3. Tradition that recommends the Ziarat on behalf of Momineen.
In the same way it is narrated from Ali bin Ibrahim Hadhrami from his father from His Eminence, Imam Musa Kazim (as) that he said in a traditional report: Thus when you approach the tomb of the Holy Prophet (S) you must do that which is necessary for you. Perform two rakats of prayer; then recite at the head of the Holy Prophet (S): Peace be on you, O Prophet of Allah from my father and mother and wife and children and all my relatives and on behalf of all the townsmen, free and enslaved, and white and black. Thus if you like you can say to anyone: I have saluted the Messenger of Allah (S) on your behalf, and you will be right in saying so.1
4. The prevalence of this practice among the scholars and common people of the Shias is to such an extent that scholars have written in detail about the reward of all this in their books of Ziarat etc. And there is no difference whether it is for Imams (as) or other believers.
5. Traditions that mention that it is recommended to do proxy Hajj and Tawaf also apply to proxy Ziarat. Since it is mentioned that if we do Ziarat on behalf of other Shias it is a meritorious deed, it also implies that we can do Ziarat of the Holy Imam (aj) on behalf of the Imam (aj) and it will be more meritorious of all as is very much clear to all.
6. The traditions of Allamah Majlisi in Biharul Anwar also proves our point: Imam Hasan al-Askari (as) sent a Zaer (visitor) for the Ziarat of Imam Husain (as) and said: One of the places where Allah likes supplication and where He accepts supplication is the Haa-e-re-Husain.2
I say: When it has been proved that it is recommended to perform Ziarat of some tombs on behalf of the Imams (as) it also implies that it is allowed and preferable for other places of visitation also, because, without any doubt there is no difference between different places of visitation.
Note: You should know that among those who have clarified and explained that it is recommended to perform Ziarat of tombs of the Holy Prophet (S) and the Holy Imams (as) by proxy for the Masoomeen and Momineen, is Muhaddith Amili who has devoted a chapter in Wasailush Shia: Chapter of recommendation of Ziarat on behalf of Momineen and Masoomeen.3 Then he has mentioned the traditional report of Dawood Surmi that he said to His Eminence, Imam Hasan Askari (as): I performed the Ziarat of your father and dedicated it to you. He replied: For that you shall get a great reward from the Almighty Allah and we are thankful to you.
I say: In this tradition there is no proof of the matter under discussion because apparently it is dedication of the reward of Ziarat and not doing it by proxy. And if we suppose that we can deny this meaning there is minimum possibility in it, and in case we take the opposite meaning, the possibility goes away.