Is specifying a dower (sadaq) a condition for the validity of marriage?

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It is recommended that marriage contracts include the specification of a dower. The Prophet, peace be upon him, always included a dower when marrying off his daughters or marrying, evidenced by his instruction to a man who had nothing to give his bride, even if it was an iron ring. The specification of the dower serves to prevent future disputes and disagreements. The validity of marriage without a specified dower is supported by the verse: {There is no blame upon you if you divorce women when you have not touched them or designated for them a dower} (Quran 2:236). Furthermore, a report states that the Messenger of Allah married a man to a woman without specifying a dower for her.