What is the evidence that the lunar mansions are 28 in number?

The jurists have agreed that the stars and the crescent moons are signs used to determine the Qibla and prayer times, and that learning about them is permissible, citing the Almighty's saying: "{And landmarks. And by the star they are guided}." It is permissible to learn what can be known through sensation, observation, or calculation, such as the names of the planets, the lunar mansions, and the twelve zodiacal signs. The zodiacal signs are twelve, and the moon's journey in each sign is two and a third days, making twenty-eight mansions, after which it becomes concealed for two nights. The sun's journey in each sign is one month.