Imam Reza (a.s.) has informed,
"Those who cannot come for our Ziarat must visit our virtuous followers. They shall get the reward of performing our Ziarat. And those who wish to do Sileh Rahmi towards us but are unable to do so must do Sileh Rahmi towards our pious devotees. They shall be given the reward of our Sileh Rahmi."
Respect and honour for the believing brother is the same as respect and honour for the spiritual father (Imam [a.s.]). In the same way, insult and disrespect of the believing brother is equivalent to insult and disrespect to the spiritual father, (the infallible Imam [a.s.]). It is for very reason that insulting a believer brings the wrath of Allah upon us and makes us deserving of severe punishment.
We shall conclude with the prayer that Allah may give Tawfeeq to all of us for doing Sileh Rahmi and fulfilling the rights of others.
source : GREATER SINS by Ayatullah-ul-Uzma Sayed Abdul Husain Dastghaib Shirazi (r.a.)