Mu'tamirnarrated from his father, from Barakah, from Bashir binNahik, fromAbu Hurairah:
"The Prophet (ﷺ) supplicated for rain(raising hishands) until I saw or one could see the whiteness of hisarmpits." (JA)
English reference (JA): Vol. 1, Book 5, Hadith 1271 (JA)
Arabic reference (JA): Book 5, Hadith 1330 (JA)