Sunan Abi Dawud
“Umayyah, daughter of AbusSalt, quoted a certain woman of Banu Ghifar, whose name was mentioned to me, as saying: The Messenger of Allah (ﷺ) made me ride behind him on the rear of the camel saddle. By Allah, the Messenger of Allah (ﷺ) got down in the morning. He made his camel kneel down and I came down from the back of his saddle. There was a mark of blood on it (saddle) and that was the first menstruation that I had. I stuck to the camel and felt ashamed. When the Messenger of Allah (ﷺ) saw what had happened to me and saw the blood, he said: Perhaps you are menstruating. I said: Yes. He then said: Set yourself right (i.e. tie some cloth to prevent bleeding), then take a vessel of water and put some salt in it, and then wash the blood from the back of the saddle, and then return to your mount. When the Messenger of Allah (ﷺ) conquered Khaybar, he gave us a portion of the booty.”
Matched via local corpus search (Sunan Abi Dawud, local idInBook 313, narrated by a woman of Banu Ghifar via Umayyah daughter of Abu al-Salt). sunnah.com URL verification unavailable this session (search endpoint returned Cloudflare block) -- no hadith number claimed pending re-verification.