Is mentioning the Prophet, may Allah's prayers and peace be upon him, upon a foot falling asleep, as narrated from Ibn 'Umar, a legitimate act?

The narration stating that Ibn Umar's leg became numb, and a man told him, "Mention the most beloved person to you," whereupon he said, "Muhammad," or "Ya Muhammad," is weak due to defects in its chains of transmission (isnads). These defects include the presence of unknown narrators, Abu Ishaq Al-Subai'i's tadlis (concealment of defects in the isnad), and inconsistencies in the narrations attributed to him.

Even if the narration were authentic, mentioning the Prophet's name (peace be upon him) was merely a simpleذكر (mentioning/remembrance), not an istighatha (seeking help/succor). Istighatha must be directed solely to Allah. The alleviation of numbness upon mentioning the name of a beloved one was a common practice among Arabs as a remedy, as they believed that mentioning a loved one stimulated blood flow, not that it constituted seeking aid from the mentioned person.

In conclusion, this narration is not authentic and cannot be used as proof for the permissibility of istighatha with other than Allah.