What is the ruling on an employee acting as a guarantor for his company in a bank guarantee letter from a non-Islamic bank?

It is not permissible to assist in obtaining a letter of guarantee unless the transaction conforms to Sharia regulations and is free from prohibitions, along with the necessity of dealing with a usurious bank when Islamic banks are unavailable. Otherwise, it is not permissible, based on the Almighty's saying: "And cooperate in righteousness and piety, but do not cooperate in sin and aggression." And according to the Prophet's (peace be upon him) saying: "Allah has cursed the one who consumes Riba (usury), the one who feeds it, its two witnesses, and its scribe." And his saying: "Riba has seventy-three doors, the easiest of which is like a man marrying his mother."