The Virtuous Shaykh ʿAbdul ʿAzīz ar-Rajihī -May Allāh preserve him- said:
The Messenger of Allāh ﷺ used to give glad tidings to his companions on the arrival of the month of Ramadān. As narrated by Abū Hurairah -May Allāh be pleased with him-, he would say:
“There has come to you Ramadān, a blessed month, which Allāh has enjoined you to fast. In it the gates of Heavens are opened and the gates of Hell are closed, and every devil is chained up. In it is a night which is better than a thousand months; whoever is deprived of its goodness is indeed deprived.”Reported by Imām Ahmad & an-Nasā’ī
The scholars have said: This hadīth has the basis on which people congratulate one another in the month of Ramadān.