What is the ruling on marrying a widow without witnesses, given that I asked a Sheikh who said the marriage is valid, but it must be documented by the Ministry of Justice?

Marriage has pillars without which it cannot be contracted: the presence of the woman's guardian (wali) or his representative, two just witnesses, a dowry (mahr), and the صيغة ( صيغة refers to the pronouncement or the formula of consent in a marriage contract). The aforementioned marriage is invalid by the consensus of the four madhhabs if there was no witnessing at the time of the contract or at consummation. It is considered invalid by the majority of scholars and valid by the Malikis if witnessing occurred at or before consummation. Registering the marriage with the court is not a condition for the validity of the contract. If the marriage took place without the presence of the woman's guardian, it is invalid by the consensus of the four madhhabs due to the absence of the two pillars of witnessing and the guardian. One must immediately distance oneself from her before renewing the contract with its pillars. The children resulting from this marriage are attributed to the man if he believed the marriage to be valid.