وعليكم السلام ورحمة الله وبركاته

▪️If there are no two witnesses present, the contract between the guardian and the groom is still VALID (1). There are scholars who stipulate the presence of two witnesses (2), however, there is no authentic evidence to support the requirement of two witnesses (3). Nevertheless, having them is better and more appropriate, as is the current practice in Muslim countries, courts, and official transactions, whether for the marriage contract itself or for proving it. In some cases, they may even require four witnesses. Whatever the case, the presence of witnesses is preferable and better than the absence of witnesses. ▪️The conditions for these witnesses are that they must be upright, trustworthy individuals. An "upright" (عدل) person is a righteous individual whose good deeds outweigh their sins and wrongdoings (4). ▪️As for your question: "If the marriage contract was not signed at the time of the marriage, can the witnesses be replaced by others who were not present at the time of the contract?" It is not necessary for the contract to be signed at the exact time of the marriage. If it is written later, there is no harm in that. The statements of the witnesses, along with the guardian and the groom, are sufficient, and the contract can be documented at any time, even after some delay (5). While it is better to formalise the information and documents at the time of the contract, it is permissible to complete the documentation after the marriage contract has been concluded. And Allāh knows best. ___ (1) This view is founded on the fact that the hadith requiring two witnesses is considered weak. Nevertheless, scholars who support this view still consider it obligatory to announce the marriage based on the hadith: ((أعلِنوا النِّكاحَ)) ‟Announce the marriage.” [Narrated by Ibn Majah (1895), Al-Bayhaqi (15094); authenticated by Al-Albani in Sahih Ibn Majah (1549)] (2) This is the view of the majority. (3) https://t.me/madrasatuna/4452 (4) Sheikh Najeeb Ash-Shar’abi added: ‟It is required that a witness to the marriage contract be: Muslim, free, sane, of age, male, and just.” (5) Sheikh Najeeb noted: ‟It is valid as long as they witnessed the marriage contract.”