Is the marriage contract considered valid if the offer and acceptance are not explicitly stated, and the Imam merely says, "So-and-so has married so-and-so," and those present accept?

The marriage formula is a pillar without which the marriage is not valid. It consists of the offer and acceptance from both parties. There is no specific formula required for it; rather, whatever people consider a marriage is a marriage, regardless of the formula used. If the suitor says to the guardian, "Did you give her in marriage?" and he replies, "Yes," and he says to the groom, "Did you accept?" and he replies, "Yes," then the marriage is concluded, provided two witnesses are present. What some followers of Malik and Ahmad have adopted, that it is only concluded with two specific phrases, is far from their principles, because circumstantial evidence in allusive expressions makes them explicit and serves the purpose of revealing intention.