Musannaf Ibn Abi Shayba 3:5632

Mu'tamir narrated to us that he heard his father narrating that Zayd ibn Thabit, Hudhayfah, al-Hasan al-Basri, and 'Ata' did not see any harm in moisture a man finds while he is praying, except that 'Ata' said: "Unless it drips." He said: And Sa'id ibn al-Musayyib said: "If it drips onto your foot, these [scholars] do not see that he is required to repeat [the prayer] nor [perform] purification."