How can one reconcile the saying "There is no guarantor except Allah" with the Prophet's (peace be upon him) saying, "I guarantee him Paradise"?

The saying: "There is no guarantor except Allah" has not been authenticated in the Qur'an or Sunnah, but it does not contradict the Prophet's (peace be upon him) hadiths guaranteeing Paradise for those who do such-and-such. This is because he is conveying from Allah the Almighty, and his informing of this is an informing of Allah's promise. Al-Tibi likened this to a person who has a right due from another, and a guarantor steps forward to ensure that right is fulfilled. These texts depend on the fulfillment of conditions and the absence of impediments. The Prophet's (peace be upon him) informing a specific person of Paradise is an informing of what has been decreed by the Pen in Allah's eternal knowledge.