Sa'id bin Jubayr narrates from Sayyiduna Ali (may Allah be pleased with him) concerning a man who divorced his wife, then made witnesses to his taking her back, but the woman did not know of it. He (may Allah be pleased with him) said: She is the wife of the first, whether the other has consummated the marriage with her or not.
(6) Chapter: What has been narrated about taking witnesses to the taking back (raj'ah) "The chapter on making witnesses to taking back"
Allah Almighty said: "Then retain them in a good manner or part with them in a good manner, and take as witnesses two just men from among you." [Surah al-Talaq: 2]
The statement of Allah Almighty: "Retain them with goodness or separate from them with kindness, and make two people of justice witnesses." [Surah al-Talaq: 2]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الرجعة / 15187