Abdullah bin Umar reported,
The Messenger of Allah ﷺ saw some spittle on the wall facing the qiblah. He scraped it off, then turned to the people and said, "When any of you is praying, let him not spit in front of his face, for Allah 
is before his face when he prays."Ishaq said in his version of the narration, "spittle."
Ahmad 5335
Sahihقال قرأت على عبد الرحمن: مالك وحدثنا إسحاق قال أخبرنا مالك عن نافع أن
عبد الله بن عمر قال
إن رسول الله ﷺ رأى بصاقا في جدار القبلة فحكه ثم أقبل على الناس فقال إذا كان أحدكم يصلي فلا يبصقن قبل وجهه فإن الله عز وجل قبل وجهه إذا صلى قال إسحاق في حديثه بصاقا
Its isnad is sahih, and it is in Muwatta 1:200. It is a repetition of 5152. His saying, Ishaq said in a narration, "yusad," is thus in the three original manuscripts, and I think that one of the two narrations is with sin or zay, and the other with sad, so that the difference would be apparent, but it is thus established in the manuscripts with sad in both of them.