Is there a religious prohibition against the phrase "Publish, and you will be rewarded," which is written at the end of messages that contain an invitation to do good, or not?

Allah Almighty has promised a great reward and recompense in this world and the hereafter to everyone who obeys Him, and He does not break His promise, in accordance with His saying: (Our Lord, and grant us what You promised us through Your messengers and do not disgrace us on the Day of Resurrection. Indeed, You do not break the promise.) Al-Imran/ 194.

The general statement that "whoever obeys Allah, He will reward him" is true, but one cannot definitively state that a specific person will receive the reward, because only Allah knows the sincerity of intentions.

The phrase "share and be rewarded" is not a definitive statement of reward for a specific person, but rather an encouragement to do good deeds, such as inviting to guidance, as in the hadith: (Whoever invites to guidance will have a reward like the rewards of those who follow him, without diminishing anything from their rewards).

There is no harm in appending messages that call to good with the phrase "share and be rewarded," as it encourages the believer to do good and reminds them of sincerity.

One must verify the content of messages before sharing them, for not every message appended with this phrase contains sound content. It may contain weak or fabricated hadith, or call to innovation (bid'ah), or slander a Muslim, or be a scam.

Sheikh Waleed bin Abdul Rahman Al-Mahwas emphasizes the necessity of adhering to controls when sending messages, among the most prominent of which are: verifying the authenticity of what is published, warning against spreading innovations, not acting upon the weak at the expense of the authentic, and being aware of what is published to avoid increasing sins instead of good deeds.