Muwatta Malik, Book 13, Hadith 5 (USC-MSA)

Yahya related to me from Malik that he had heard that the Messenger of Allah, may Allah bless him and grant him peace, used to say, "When a cloud appears from the direction of the sea and then goes towards ash-Sham, it will be an abundant source of rain."

وَحَدَّثَنِي عَنْ مَالِكٍ، أَنَّهُ بَلَغَهُ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم كَانَ يَقُولُ ‏ "‏ إِذَا أَنْشَأَتْ بَحْرِيَّةً ثُمَّ تَشَاءَمَتْ فَتِلْكَ عَيْنٌ غُدَيْقَةٌ ‏" ‏ ‏.‏

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also referenced under: Book 13, Hadith 456 (In-Book)