In saluting Imam Hussein (PBUH) in Ashura visitation text, "Assalamu Ala Al Hussein wa ala Ali ibnul Hussein…

Answer

In the name of Allah, there is no doubt that there is preference of Al-Taf martyrs over other martyrs. That is why Hamza Ibn Abdulmutalib (PBUH) is called the master of the martyrs out of those who died in Battle of Uhud. As for not mentioning Abal Fazl (PBUH), the reason is - Allah knows best- that this visitation text was created when the master of believers (PBUH) did the visitation and it was remotely done. That is why other than the master of martyrs was mentioned in general. Mentioning his name, Ali Al-Akbar (PBUH), specifically is a reference to his privilege over the rest of the martyrs from among the relatives of the Master of Martyrs (PBUT), and Abal Fazl Al-Abbas (PBUH) also entered into this general address. Allah knows best.