Whoever intends to slaughter a sacrificial animal should not take from his hair, or nails until he offers his Ud-hiyah
Whoever wants to offer Ud-hiyah should refrain, during the first ten days of Dhul-Hijjah, from removing any hair, clipping any nails, or cutting anything of the skin of the body until the Ud-hiyah is slaughtered. There is a Sahih (authentic) Hadith in this regard which was narrated by
Um Salamah attributing it to the Prophet:
When the (first) ten (days of Dhul-Hijjah) starts and anyone of you intends to offer Ud-hiyah, let them not cut anything of their hair or nails until they sacrifice it.
Muslim in his Sahih [Authentic Hadith Book]) Such a person is not considered in the state of Ihram; rather, this is a specific ruling for them.Cutting hair or clipping nails out of forgetfulness or ignorance has no consequences because Allah (Glorified be He) says:
Our Lord! Punish us not if we forget or fall into error
It was authentically reported that the Prophet (peace be upon him) said about the Tafsir (explanation/exegesis of the meanings of the Qur'an) of this Ayah (Qur'anic verse) that
Allah said: 'I did.'
(Part No. 10; Page No. 435) May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.