The Prophet ﷺ saw some phlegm on the qiblah wall of the mosque and scraped it off with a small stone or something similar. He then said, "When one of you stands to pray, let him not spit in front of himself, nor to his right, for an angel is on his right. Rather, let him spit to his left or beneath his left foot."
حدثنا عبد الرزاق حدثنا معمر عن الزهري عن حميد بن عبد الرحمن
أن النبي ﷺ رأى نخامة في قبلة المسجد فحتها بمروة أو بشيء ثم قال إذا قام أحدكم إلى الصلاة فلا يتنخمن أمامه ولا عن يمينه فإن عن يمينه ملكا ولكن ليتنخم عن يساره أو تحت قدمه اليسرى
Its isnad is sahih. Bukhari also narrated it, in similar form but abridged, 1:428-729, through Abdul-Razzaq, from Maamar, from Hammam bin Munabbih, from Abu Hurairah. He also narrated its meaning, 1:426-427, twice, through Zuhri, from Humayd bin Abdul-Rahman, from Abu Hurairah and Abu Saeed Khudri. Something similar in meaning has already passed at 7399, through another route from Abu Hurairah. See also 7522.Marwa is a white, glistening stone.