(Imām Bukhārī narrates): Qutaibah ibn Sa'īd narrated to us, he said: Laith narrated to us, from Nāfi', from Ibn 'Umar, may Allāh be pleased with them both, he narrates that:

the Prophet ﷺ saw phlegm lying towards the qiblah of the mosque, at that time he was praying in front of the people. So he scraped it off, then he turned towards the people and said: When any one of you is in prayer, Allāh the Exalted is in front of his face, so let not any one of you spit in front of his face in prayer.

And this hadith has been narrated by Mūsā ibn 'Uqbah and Ibn Abī Rawwād, from Nāfi'.