Why are phrases such as "What Allah wills and you will" or "I have relied upon Allah and upon you" prohibited in order to preserve Tawhid (monotheism), while saying "my beloved" to a human being is not prohibited, even though love for a human is relative and not absolute like love for Allah?

Verbal association between the Creator and the created is prohibited, such as saying: "Whatever Allah wills and you will," in order to protect monotheism and out of reverence for Allah. This is because the conjunction "wa" (and) implies combination and association, and suggests equality between the will of the servant and the will of Allah.

Whereas, saying: "Whatever Allah wills then you will" is permissible, because "thumma" (then) implies sequence, not association, and does not necessitate equality.

There is no harm in making a matter dependent solely on the servant's will, such as saying: "If you wish," which is frequent in the Sunnah.

The prohibition of association with "wa" pertains to predetermined, creative matters like will and reliance. As for other matters, such as love and obedience, association with "wa" is permissible, like saying: "I love Allah and His Messenger."

The correct approach in this matter is to differentiate, not to impose an absolute prohibition on verbal association using "wa".