Authentic Supplication Number 152.

Salem related that his father said: A Bedouin came to the Prophet  and said: O Messenger of Allah my father used to maintain the ties of kinship, and he was so, and he was so. So where is he? He said: In Hell-fire. He said: It was as if that disturbed him, so he said: O Messenger of Allah, where, then, is your father? The Messenger of Allah  then said: Wherever you pass by the grave of a polytheist give him tidings (171) of Hell-fire. He said: The Bedouin later accepted Islam and said:The Messenger of Allah  has given me an assignment. I would not pass by the grave of a Kafir except that I would give him tidings of Hell-fire.

Footnotes.
(171) Allah The Exalted said "And proclaim a grievious chastisement to those who reject Faith" Surah Bara'ah (#9), V.3.

Reporters.
At-Tirmidhi said it was comely and Al-Albani agreed. Al-Albani said An-Nisa'ee and Ibn Majah also reported it with sound ascription and he included it in The Authentic of Good Sayings.