I heard the Messenger of Allah (ﷺ) say: When a Muslim supplicates for his absent brother the angels say: Amin, and may you receive the like.
Sunan Abi Dawud Book 8, Hadith 119
← Previous Hadith A woman said to the Prophet (ﷺ): Invoke blessing on me as well as on my husband. The Prophet (ﷺ) said: May Allah send blessing on you and your husband.

Sunan Abi Dawud Book 8, Hadith 118 Next Hadith → The Prophet (ﷺ) said: The supplication which gets the quickest answer is that made by one distant Muslim for another.

Sunan Abi Dawud Book 8, Hadith 120