"Urvatu'l-Vuthqá" is a Qur'anic term indicating the belief in the oneness of God (Fadil Mazandarani in his encyclopedic work, Asráru'l-Athár Vol.IV Pp 333-334). In the English translation of Kitáb-i-Aqdas, #117 it is translated as "Sure Handle". Bahá'u'lláh in one of His Tablets has the following statement: "This Covenant of God is "Urvatu'l-Vuthqá". Abdu'l-Bahá in one of His Writings says," Urvih-yi Vuthqa revealed, from the foundation of the world,in sacred books and scriptures of the past is the covenant of God." (same source as above) "Urvatu'l-Vuthqá" in Íqán refers to the veerses or words of God.
In another occasion that this term is used is in the Tablet of the World (Lawh-i-Dunyá):
"The aforesaid person hath written such things concerning this people in the Egyptian press and in the Beirut Encyclopedia that the well-informed and the learned were astonished. He proceeded then to Paris where he published a newspaper entitled Urvatu'l-Vuthqá [The Sure Handle] and sent copies thereof to all parts of the world. He also sent a copy to the Prison of Akká, and by so doing he meant to show affection and to make amends for his past actions. In short, this Wronged One hath observed silence in regard to him. We entreat God, the True One, to protect him and to shed upon him the light of justice and fairness."
(Bahá'u'lláh: Tablets of Bahá'u'lláh, Page: 95)
The person referred to in the Tablet to the World is Siyyid Jamálu'd-Din Afghani, a notorious religious and political reformer in the 19th Century Middle East. According to this statement by Bahá'u'lláh and also as Abdu'l-Bahá has related, he was a deceitful and hypocritical person (muza-ver) and while he was in Istanbul he was instigating and plotting against Bahá'u'lláh and his followers. (Fadil Mazandarani, Asráru'l-Athár Vol.III p. 42)