Is the story of Khalid ibn al-Walid keeping a lock of the Prophet’s — may Allah’s prayers and peace be upon him — hair in his helmet, and it falling and him retrieving it, authentic and found in sound Prophetic hadiths or sira hadiths, and how is it viewed in light of the Qur’an, the Sunnah, and the Oneness of God?

Blessing oneself with the relics of the Prophet, peace and blessings be upon him, such as his hair, sweat, and what he left over (su'r), is permissible by the agreement of the scholars. This is specific to the Prophet, peace and blessings be upon him. As for seeking blessings from the relics of others, it is an innovation (bid'ah) and a means to shirk (definition) (polytheism).

A story has been narrated about Khalid ibn al-Walid that he used to keep a hair from the Prophet's forelock in his cap, and that he was granted victory in battle through it. However, this hadith (definition) is weak due to a break in its chain of narration.

Even assuming the story is authentic, the relics of the Prophet, peace and blessings be upon him, no longer exist in a verifiable form that can be attributed to him.