Ikrimah narrates from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that zihar and divorce do not occur before marriage.
(b) In the Book of Divorce it is narrated from the Prophet (peace and blessings be upon him), Sayyiduna Ali (may Allah be pleased with him) and Sayyiduna Ibn Abbas (may Allah be pleased with them both): "There is no divorce before marriage, and zihar has the same meaning."
The opposite of this has been narrated from Umar bin al-Khattab (may Allah be pleased with him) with a mursal chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الظهار / 15251
Al-Qasim bin Muhammad (may Allah have mercy on him) said that a man declared a woman to be like his mother if he married her; Sayyiduna Umar (may Allah be pleased with him) said that he should marry that woman but not go near her before paying the expiation for zihar.
This is munqati' (broken); al-Qasim bin Muhammad did not meet Umar bin al-Khattab (may Allah be pleased with him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الظهار / 15252