(a) Rabi' bin Khuthaym (may Allah have mercy on him) narrates that Abdullah bin Mas'ud (may Allah be pleased with him) saw a louse on a man's garment in the mosque, so he took it and buried it in the pebbles, then recited: "Have We not made the earth a receptacle, for the living and the dead?" [Surah al-Mursalat: 25-26]
(b) Something similar is reported from Mujahid and Ibn al-Musayyib (may Allah have mercy on them both): that one should bury it, just like phlegm.
(c) It has been narrated to us on the authority of Malik bin Yakhamir (may Allah have mercy on him): I saw Mu'adh bin Jabal (may Allah be pleased with him); he would kill lice and fleas while in prayer.
(d) Al-Hasan (may Allah have mercy on him) said: There is no harm in killing lice during prayer, but one should not start fidgeting idly.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3609