And as they cried out, and cast off their clothes, and threw dust into the air, Acts 22:23
Easterners, when not at work, generally wear expensive and heavy robes. The outer robe or garment usually worn on such occasions is called abaya. It is an expensive and heavy garment which many men wore as a token of dignity and not because of necessity. When men enter a house they remove their abayas. Likewise, when at church or mosque, the robe and shoes are removed and set aside. Then again, when people quarrel, they throw off their garments to avoid getting them soiled. A man would almost rather have his body stabbed than have his good robe destroyed.
These men cast off their robes as a signal of protest and of readiness to attack Paul, as in the case of the stoning of Stephen.
Dust is symbolic of mourning, or of repudiation of some act wrongly committed. When a man is killed, his relatives throw dust over their heads and garments. Likewise, when some awful deed is committed, Easterners lose their tempers and act almost mad. Paul, in the eyes of the Jews, had defiled the Temple by bringing Gentiles into it. The priests and religious men tried to magnify the seriousness of the incident in order to incite the crowd and bring about the arrest of Paul.
(Lamsa, George. New Testament Commentary, A.J. Holman Co., Philadelphia: 1945, pgs 163-164)