I saw the Messenger of Allah ﷺ spit out phlegm and rub it with his left foot.
أخبرنا سويد بن نصر قال أنبأنا عبد الله عن سعيد الجريري
رأيت رسول الله ﷺ تنخع فدلكه برجله اليسرى
No references are available.
Muslim narrated it in the Book of Masjids, chapter on the prohibition of spitting in the masjid, etc., no. 554/59, from the hadith of Jareeri with this wording, and it is also in Kubra, no. 806.