Is wearing a silver ring, custom-made in the month of Rajab, with Arabic numerals engraved on the inside, considered part of Islam?

It is permissible for both men and women to wear a silver ring, by the consensus of scholars, and the proof for this is the action of the Prophet, peace and blessings be upon him.

As for dedicating the month of Rajab to wearing a ring, this is something that has no basis in the Sharia. Whoever does so believing it to be a means of drawing closer to Allah or that it possesses a virtue has innovated.

One should also be wary of engraving on it what is claimed to bring good luck or ward off the evil eye, envy, and the like.

The original ruling for wearing a ring and engraving upon it is permissible. What is forbidden is to worship through it, or to dedicate its wearing to a specific time, or to seek blessings from it, or to make it an amulet.