What is the ruling on muezzins calling out before Fajr to alert people to the approaching time of Imsak, using phrases such as, "O believers, abstain from food and drink"?

The muezzin's statement, "Refrain from food and drink," intended to signify abstaining from things that invalidate the fast, is not based on any legal (Sharia) evidence and was not known among the Salaf (pious predecessors). Therefore, it is better to avoid it. The best guidance is the guidance of the Prophet, peace and blessings be upon him: "Whoever introduces into this matter of ours that which is not from it, it is rejected."