✅Answer: Please pay attention to the following narrations:

1 عَلِيُّ بْنُ الْحُسَيْن الْمُرْتَضَى فِي رِسَالَةِ الْمُحْكَمِ و الْمُتَشَابِه نَقْلًا مِنْ تَفْسِير النُّعْمَانِيِّ بِإِسْنَادِه عَنْ عَلِيٍّ قَالَ: وَ أَمَّا حُدُودُ الصَّوْمِ فَأَرْبَعَةُ حُدُودٍ أَوَّلُهَا اجْتِنَابُ الْأَكْلِ و الشُّرْبِ وَ الثَّانِي اجْتِنَابُ النِّكَاحِ و الثَّالِثُ اجْتِنَابُ الْقَيْ ءِ مُتَعَمِّداً و الرَّابِعُ اجْتِنَابُ الِاغْتِمَاسِ فِي الْمَاءِ و مَا يَتَّصِلُ بِهَا وَ مَا يَجْرِي مَجْرَاهَا مِنَ السُّنَنُ كُلِّهَا

📚 Bihar, Vol. 93, p. 64

Amir al-Mu'minin (peace be upon him) said: 'The limits of the fast are four things: The first is avoiding eating and drinking; the second is avoiding intercourse; the third is avoiding intentional vomiting; and the fourth is avoiding submerging in water and whatever is connected to all the customs and practices that are considered to be like them.'

✅The main things that invalidate the fast are limited and specified. However, according to the end of the hadith, there are also customs that are connected to those invalidators and are considered to be like them. For example, please pay attention to the following narration:

2 سُلَيْمَان بْنِ حَفْص الْمَرْوَزِيِّ قَال سَمِعْتُهُ يَقُولُ إِذَا تَمَضْمَضَ الصَّائِمُ فِي شَهْرِ رَمَضَانَ أَوِ اسْتَنْشَقَ مُتَعَمِّداً أَوْ شَمَّ رَائِحَةً غَلِيظَةً أَوْ كَنَسَ بَيْتاً فَدَخَلَ فِي أَنْفِهِ و حَلْقِهِ غُبَارٌ فَعَلَيْهِ صَوْمُ شَهْرَيْنِ مُتَتَابِعَيْن فَإِنَّ ذَلِكَ لَهُ مُفَطِّرٌ مِثْلُ الْأَكْلِ و الشُّرْب و النِّكَاح

📚 Al-Tahdhib, Vol. 4, p. 214

Sulayman ibn Hafs says: I heard (the Imam, peace be upon him) say: 'When a fasting person in the month of Ramadan intentionally rinses his mouth and nose, or smells a strong odor, or sweeps a room and dust enters his nose and throat, he is obligated to fast for two consecutive months, because these matters, just like eating, drinking, and intercourse, are invalidators of the fast.'

✅Rinsing the mouth and nose has details that will be examined in their proper place.

✅In the above narration, we see that the Imam (peace be upon him) introduces some matters that are considered to be like eating and drinking. But a question that arises and a great doubt that is created is:

'Is the smoke from a cigarette that we intentionally inhale into the throat and lungs considered eating or drinking, or is it considered to be like drinking and eating?'

✅Due to the relevance of this question on one hand, and to avoid speaking without knowledge on the other hand, we need a very important principle in Shi'a jurisprudence to know our duty in such cases, and that principle is 'precaution':

3 عَبْد الرَّحْمَن بْن الْحَجَّاج قَالَ: سَأَلْتُ أَبَا الْحَسَن عَنْ رَجُلَيْن أَصَابَا صَيْداً وَ هُمَا مُحْرِمَانِ الْجَزَاءُ بَيْنَهُمَا أَوْ عَلَى كُلِّ وَاحِدٍ مِنْهُمَا جَزَاءٌ قَالَ لَا بَلْ عَلَيْهِمَا أَنْ يَجْزِيَ كُلُّ وَاحِدٍ مِنْهُمَا الصَّيْد.... فَقَالَ إِذَا أَصَبْتُمْ مِثْلَ هَذَا فَلَمْ تَدْرُوا فَعَلَيْكُمْ بِالاحْتِيَاطِ حَتَّى تَسْأَلُوا عَنْهُ فَتَعْلَمُوا.

📚 Al-Kafi, Vol. 4, p. 391

Imam Al-Kazim (peace be upon him) said regarding two pilgrims in ihram who hunted and did not know whether both of them had to pay expiation or only one of them: 'When you are afflicted with such matters and you do not know, you must be cautious until you ask about it and gain knowledge.'

4 عن أَبِي شيْبَة عَنْ أَحَدهِما قَالَ فِي حَدِيثٍ الْوُقُوفُ عِنْد الشُّبْهَةِ خَيْرٌ مِنَ الِاقْتِحَام فِي الْهَلَكَة

📚 Al-Zuhd, p. 19

Abu Shaybah narrated from Imam Al-Baqir or Imam Al-Sadiq (peace be upon them) that they said: 'Hesitation in the face of doubts is better than suddenly falling into destruction.'

✅Based on the principle of precaution, which is very much needed, especially in this time of the Imam's occultation and our lack of access to him, and which has been commanded in numerous narrations, when we are at a loss regarding the entry of cigarette smoke into the throat and lungs for a fasting person, we cling to this principle by the command of the Ahl al-Bayt (peace be upon them), and although the cigarette itself is worthy of avoidance because it is an instance of extravagance, we specifically avoid it during the fast lest there be a flaw in the obligatory fast and lest we suddenly fall into the destruction of the invalidation of the fast.

✅It must be known that the command for precaution in cases of doubt is like the direct rulings of the Ahl al-Bayt (peace be upon them) and can in no way be shirked.

✅Intentionally inhaling cigarette smoke into the throat and lungs during the fast severely puts our fast at risk and in a state of extreme doubt, and mentioning it as a doubt is merely because the exact phrase is not in the narrations, but its appearance cannot be taken out of the category of being an instance or being similar to eating or drinking.