[According the ḥanbalī madh`hab], it is not from the Sunnah for a fasting person to use the siwāk afternoon [i.e. after ẓuhr]. We say ‘afternoon’ meaning the sun has begun inclining towards the west. The sun rises from the east until it reaches its apex [or zenith], then begins to descend [towards the west], we say then afternoon has begun.
The scholars say: the indication of the beginning of afternoon is to erect a stick in the ground and watch it, as long as the shadow projected by the stick decreases [in size], the sun has not reached its zenith. Whenever the projected shadow begins to increase in size even by a hair, it means the sun has reached its zenith and has begun its descent.
The most well-known opinion from the [ḥanbalī] madh`hab is that using the siwāk in the afternoon [i.e. after ẓuhr] is disliked for a fasting person. The evidence of this is:
In the morning, it is liked for him to use a dry [siwāk] but permissible for him to use a moist one. Hence, they have made the siwāk for the fasting person into three categories of use:
As for its use in the morning for a fasting person, their evidence is the general passages encouraging its use.
As for the usage of a moist [siwāk] and its ruling of permissibility, it is due to its moistness they fear that some of the taste of the siwāk may escape his mouth, making it to his throat and thus make his fasting deficient. It is because of this that the Prophet (ﷺ) said to Laqīṭ ibn Ṣabirah: ‘And rinse your mouth thoroughly [when performing wuḍūʿ] except when in a state of fasting.’
As for the ruling of karāhah [dislike] for its use in the afternoon, its evidence is the aḥādīth and reasoning aforementioned that prove that it is disliked.
The author of ‘Al-Iqnāʿ’- which is from the later books of the ḥanbalī madh`hab and frequently expresses the final opinion of this school of thought, states: ‘The evidence for this [opinion] is more apparent.’ This is also the opinion chosen by Shaykh al-Islām Ibn Taymiyyah.
Their evidence is the general passages encouraging the use of the siwāk like the ḥadīth of Āʾishah (may Allāh be pleased with her) in which the Prophet (ﷺ) made no exceptions. What has been related in a general all-encompassing way should be left as is, unless a valid exception arises. For this [hadīth], there exists no such exception.
As for the (aforementioned) ḥadīth of ʿAlī, it is weak. Thus, it is not strong enough to cause an exception for that which is related in an authentic narration. This is because that which is weak is not valid evidence [in and of itself]. Thus, we cannot extract a valid ruling from such a passage. Then, applying an exception to an established ruling is a ruling itself. In doing so, we are extracting a ruling from its original all-encompassing state and applying it instead to a specific situation. To do such a thing, we need clear evidence that supports this extraction. Otherwise, we cannot accept this [exceptional ruling].
As for their reasoning, it is not sound for several reasons:
The correct opinion in this matter is that siwāk is Sunnah at all times, even for the fasting person. This is supported by the ḥadīth of ʿĀmir ibn Rabīʿah, narrated by al-Bukhārī without a chain of narrators:
‘I saw the Prophet (ﷺ) use the siwāk while he was fasting so many times that I cannot enumerate or count them.’
Source: Al-Sharḥ al-Mumtiʿ 1: 148-151
Translated by: Riyāḍ al-Kanadī