How sound is the circulating saying: "Forty prayers from a stranger are answered," and what is the ruling on propagating it?

We do not know of any basis for this phrase. However, it is authentically established in the Sunnah that there are those whose supplications are answered, such as the traveler, the parent, and the oppressed. The Prophet, peace and blessings be upon him, said: "Three supplications are answered without doubt: the supplication of the oppressed, the supplication of the traveler, and the supplication of a parent against his child." This was not specified as forty supplications. Therefore, it is not permissible to propagate this statement unless there is a basis for it.