To what extent is the saying "Three things have no existence: the ghoul, the phoenix, and the loyal friend" true, and what is the ruling of Islamic law regarding the existence or non-existence of a friend?

The ghoul and the phoenix are used as examples of something that does not exist. As for the loyal friend, he exists but is precious and rare. Islam encourages brotherhood and taking friends, but brotherhood must be built on sound foundations, such as love for the sake of Allah, so that it may yield loyalty and advice; otherwise, it will vanish when its cause vanishes.