How can one increase the "tahjil" (the white blazes on a horse's legs, metaphorically referring to the نور - light - on the limbs of those who perform Wudu') in ablution by washing part of the head and neck along with the face, the hands up to the shoulders, and the feet up to the knees?

It is established in the authentic Hadith (definition) that the Ummah of Muhammad (peace and blessings be upon him) will be called on the Day of Resurrection as "ghurran muhajjalin" due to the effects of wudu', meaning that their faces, hands, and feet will have a shimmering light. Scholars have differed regarding extending beyond the obligatory limits in wudu':

1. The Majority (excluding Malikis): They consider it desirable to extend beyond the obligatory limits, citing the hadith: "Whoever can lengthen his ghullah (forehead's radiance) should do so." This includes extending the washing beyond the obligatory limits to the upper arms and shins, ensuring their complete washing, and washing a small part of the head and the part of the neck adjacent to the face. 2. The Malikis and those who agreed with them (such as Ibn Taymiyyah and Ibn al-Qayyim): They do not consider such extension desirable, arguing that: Extending beyond the obligatory limits requires evidence. The description of the Prophet’s wudu' (peace and blessings be upon him) involved washing the limbs only up to the obligatory limits. The Ayat of wudu' specifies the obligatory limits (elbows and ankles). The phrase "Whoever can lengthen his ghullah should do so" is an insertion from the words of Abu Hurairah, not from the words of the Prophet (peace and blessings be upon him). The ghurrah (radiance) is on the face and cannot be extended, and it is not desirable to extend the hajalah (radiance on the limbs).

Conclusion: The Sunnah (definition) is to wash the hands up to the elbows (including what is permissible on the upper arm) and to wash the feet and ankles (including what is permissible on the shin), as this is what is authentically reported from the Prophet (peace and blessings be upon him).