The Prophet ﷺ prayed for rain until I saw, or it was seen, the whiteness of his armpits.
أن النبي ﷺ استسقى حتى رأيت- أو رئي- بياض إبطيه.
Ibn Majah (1271) narrated it, and this is his wording, as did Ahmad (8830), and Ibn Khuzayma (1413) graded it sahih. All of them narrated it through the route of Sulayman Taymi, from Baraka (who is Abu Walid), from Bashir bin Nuhayk, from Abu Hurairah, who related it. Its chain of transmission is sahih.On this subject there is also a report from Sahl bin Saad, who said, "I never once saw the Messenger of Allah ﷺ raise his hands while supplicating, whether on his pulpit or elsewhere, but I did see him say, like this," and he pointed with his index finger and joined his middle finger to his thumb. Abu Dawud (1105) narrated it, as did Ahmad (22855), and Ibn Khuzayma (1450), Ibn Hibban (883), and Hakim (1/535-536) graded it sahih. All of them narrated it through various routes from Abdul-Rahman bin Ishaq, from Abdul-Rahman bin Muawiya, from Ibn Abu Dhubab, from Sahl bin Saad, who related it.Hakim said, "This is a hadith sahih in its chain of transmission." I say, in its chain is Abdul-Rahman bin Muawiya, who is Ibn Huwayrith Ansari Zurqi Madani, and he is among those whose sole narration cannot be relied upon. Abdul-Rahman bin Ishaq is Ibn Abdullah bin Harith Qurashi Amiri Madani. And Ibn Abu Dhubab is Abdullah bin Abdul-Rahman bin Harith.