What is the evidence for one who takes the opinion of fasting according to the horizon in one’s region?

Kuraib narrated that Umm al-Fadl sent him to Muawiyah in ash-Sham. He said, “I came to ash-Sham and completed the errand. Then the new crescent of Ramadan was sighted while I was in ash-Sham. I saw the new crescent on the night of Friday, then I went to al-Madina at the end of the month. ‘Abdullah ibn ‘Abbas asked me about the sighting of the moon and said, “When did you see it?” I said, “We saw it on the night of Friday.” He said, “You saw it on the night of Friday?” I said, “Yes, and the people saw it and started fasting, and so did Muawiyah.” He said, “But we saw it on the night of Saturday, so we will continue fasting until we have completed thirty days or we see it.” I said, “Will you not be content with the sighting of Muawiyah and his companions?” He said, “No, this is what the Messenger of Allah enjoined upon us.”
Ibn ‘Abbas did not go by the sighting of the people of ash-Sham, and the people of a region do not have to go by the sighting of the people of another region.