Is it permissible for a husband to take back his wife in the presence of only the spouses without witnesses, knowing that she had been divorced with a clear pronouncement?

The jurists differed on two opinions regarding the requirement of attestation for a revocable divorce (raj'ah):

1. Obligation of attestation: They based their argument on the Almighty’s saying: "And bring to witness two just men from among you" (Quran 65:2); and to ensure inheritance. 2. Recommendation of attestation (the opinion of the majority): They used the same verse as evidence, interpreting the command as a recommendation, and arguing that a revocable divorce does not require the woman's acceptance. They also pointed out that the Prophet, peace and blessings be upon him, did not mention attestation in Ibn Umar's hadith.

The more preponderant opinion is the second one (the recommendation of attestation). Accordingly, your revocable divorce is valid, and it is recommended for you to have it attested.