Maymun bin Mihran (may Allah have mercy on him) said: I was sitting with Abdullah bin Abbas (may Allah be pleased with him), and a man sat with him; I had never seen anyone with longer hair than him. He said: I have entered ihram with this hair on me. Abdullah bin Abbas (may Allah be pleased with him) said: Wrap up the part of it that is below the ears. He said: I kissed a woman who was not my wife. He said: Your mouth has committed fornication. He said: I saw a louse and threw it away. He said: That is a lost thing that is not sought.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10063
Uyaynah bin Abd al-Rahman bin Jawshan narrates from his father that a man said to Sayyiduna Abdullah bin Abbas (may Allah be pleased with him): May I scratch my head while I am in the state of ihram? He said: Sayyiduna Abdullah bin Abbas (may Allah be pleased with him) put his hand into his hair while he was in ihram and scratched his head vigorously, and said: As for me, I do it like this. He said: What do you think if I kill a louse? He said: You have gone far off! What is a louse? It makes no difference to the scratching of your head, it was not the louse you intended, and you have been forbidden only from killing game.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10064
Salim bin Abdullah narrates from his father that a man came to him and said: I killed a louse while I was in the state of ihram. Ibn Umar (may Allah be pleased with him) said: That is the most trivial of killings.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10065
It is narrated from Sayyiduna Ibn Umar (may Allah be pleased with him) that he used to use the tooth-stick (miswak) while fasting and look in the mirror while in the state of ihram, and he would say: The person in ihram may scratch his head, as long as he does not kill lice or wound the skin of his head.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10066
Al-Hurr bin al-Sayyah (may Allah have mercy on him) said: I heard Ibn Umar (may Allah be pleased with him) say about a louse that a person in ihram kills: He should give in charity a piece of bread or a handful of food. [Sahih: Recorded by Ibn al-Ja'd: 570]
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 10067