Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa. – Volume 18, Page 11, Fatwa No.4525, Question 1
Question: When a man divorces his fourth wife, and wishes to replace her with a[nother] wife, does he have to wait [for the passing of] the duration of the ‘iddah of the divorced [fourth] wife?
Response: It is prohibited for the one who has divorced his fourth wife to marry another until the divorced (fourth) wife comes out of her ‘iddah.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet Muhammad (sal-Allaahu `alayhi wa sallam) and his family and his companions.