Tasmiyah before ghusl

ذهب الحنفية والشافعية إلى أن التسمية سنة من سنن الغسل، وعدها المالكية من المندوبات

The Hanafi and Shaafi'i schools of thought have said that the tasmiyah is a Sunnah of ghusl. The Maaliki school considers it a manduub [recommended] act.

وذهب الحنابلة إلى وجوب التسمية لقول النبي صلى الله عليه وسلم: لا وضوء لمن لم يذكر اسم الله عليه (1) قياسا لإحدى الطهارتين على الأخرى

The Hanaabilah have adopted the opinion that the tasmiyah is waajib based on the saying of the Prophet (sallallaahu alayhi wa sallam): There is no wuduu' for the one who does not mention the Name of Allaah on it. [1]

They have made Qiyaas of for one form of Tahaarah over the other [i.e. the hadiith talks about wuduu. They have made Qiyaas and extended the ruling to ghusl].

قال ابن قدامة: ظاهر مذهب أحمد أن التسمية مسنونة في طهارة الأحداث كلها، وعنه أنها واجبة فيها كلها: الغسل والوضوء والتيمم

Ibn Qudaamah said: The Zaahir of the Madhab of Ahmad is that tasmiyah is masnuun in all forms of Tahaarah al-'ahdaath and from him is a narration that it is waajib in all of them, ghusl, wuduu, and tayammum.

[1] Ibn Hajar indicated that there is 'inQiTaa' in the chain of narrators of this hadiith. Then he brought forth shawaahid for it and said: The Zaahir is that when all the hadiith are taken into account they strengthen it and indicate that it has a basis.

Reference(s):

Kuwaiti Encyclopedia of Fiqh

Volume 31 Page 212