SHAFAQNA – The Grand Ayatollah Sistani answered a question about crying whilst performing Salaat.
Question: Is there a problem to cry when performing Salaat?
The Grand Ayatollah Sistani: According to Wajib precaution, one of the acts which invalidates Salaat is to cry on purpose with or without sound for worldly cases; but there is no problem to cry loud or quietly for the fear of God, or for the love of God, or to cry for the hereafter, in fact it is one of the best deeds. Also there is no problem to cry for asking worldly wishes from God whilst showing humility towards God; and also there is no problem crying for the sufferings of Ahlul Bait (AS).
Source: PERSIAN SHAFAQNA