Allah Almighty, and He is the most truthful of all who speak, said: "Then do not prevent them from marrying their (former) husbands." [Surah al-Baqarah: 232]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / Q13790
Hasan (al-Basri) (may Allah have mercy on him) said concerning the saying of Allah Almighty: "Do not prevent the women who wish to marry their husbands." [Surah al-Baqarah: 232] that Sayyiduna Ma'qil bin Yasar (may Allah be pleased with him) told him that this verse was revealed concerning him. (He said:) I married my sister to a man, and he divorced her. When her waiting period ended, he proposed to her again. I said to him: I married you (to her) and honoured you, but you divorced her, and now you have come proposing to her again. By Allah! You will never go back to her. The narrator said: There was nothing wrong with the man, and the woman also wanted to return (to him). So Allah Almighty revealed this verse. I said: O Messenger of Allah (peace and blessings be upon him)! Now I have married her to him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13790
Sayyidah Aishah (may Allah be pleased with her) said: I heard the Messenger of Allah (peace and blessings be upon him) say: "Any woman who marries without the permission of her guardians, her marriage is void, her marriage is void. If (the husband) has had intercourse with her, then the mahr is hers. If the guardians dispute among themselves, then the ruler is the guardian of the one who has no guardian."
(b) Mujalid narrates from al-Sha'bi, and he from Sayyiduna Ali and Sayyiduna Abdullah (may Allah be pleased with them both) and Shurayh, that marriage is not valid without a guardian, except for a woman whose guardian prevents her (from marrying); she may then go to the ruler or the judge.
(c) Ziyad bin Ilaqah said that Sayyiduna Uthman bin Affan (may Allah be pleased with him) wrote: If a suitable match (kuf') is available, then tell the woman's father to marry her off; and if he refuses, then you marry her off.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13791