In Vedas, Shastras, Puranas, Parmartha Smriti Shri Hari Bhakti Vilas, and in various other dharma-shastras, the glories of Chaturmasya-vrata has been described. It’s been mentioned that one gets the benefit of living in heaven for eternity by observing Chaturmasya-vrata, like this, there are various other worldly benefits mentioned in karma-kāṇḍa shastras. Shastras not only prescribe this Vrata for those who keep it for worldly benefit, but also for gyāni (eka-daṇḍi) and bhakta (tri-daṇḍi). There is an arrangement of keeping Chaturmasya-vrata for persons belonging to all the ashrams (Brahmacharya, Gṛihastha, Vanaprastha and Sannyasa). Though the rituals or the process of observing Chaturmasya-vrata for bhakta, gyāni and karmi are different, everyone who follows sanātan-dharma observes the vrata. All three; karmis, gyānis and bhakta endeavor to perform a lot of penance during observance of the vrata but sādhaka-bhakta observe it with the sole objective of engaging their senses fully for the service of bhakta and Bhagavan. They do not observe this vrata for getting material benefit and heavenly planets like karmi, or with the desire of getting salvation like the gyāni do.

Chaitanya Mahaprabhu who appeared in this world to deliver the fallen soul of Kaliyuga also observed Chaturmasya-vrata at Venkat Bhatt’s house when He was on His South India tour. He also observed this vrata when He was in Puri in the company of devotees being fully engaged in Krishna-katha. The evidence of this is mentioned in Chaitanya Charitamrita which is compiled by Sri Krishnadas Kaviraj Goswami.

ei-mata mahāprabhu bhakta-gaṇa-saṅge
cāturmāsya goṅāilā kṛṣṇa-kathā-raṅge
(Sri Chaitanya Charitamrita 10.133)

“Thus Sri Chaitanya Mahaprabhu spent the entire period of Chaturmasya in the happiness of discussing topics of Krishna with His devotees.”

Those who are incapable of observing the Chaturmasya-vrata, whether a householder or a renunciate, should definitely observe Kartika-masa-vrata, which is one amongst the important sixty-four limbs of devotion. This does not mean that for devotees, the observance of Chaturmasya-vrata is optional, as the above mentioned instruction is applicable only for persons who are incapable of performing vrata for four months.

The details about the timing of observing Chaturmasya-vrata is given in Varaha Purana.

āṣāḍha śukladvādaśyām paurṇamāsyāmathāpi vā
Cāturmāsya vratārambham kurjyyāt karkaṭa samkrame
abhābe tu tulārkehapi mantreṇa niyamam vratī
kārtike śukladvādaśyām vidhivattat samāpayet

One can follow anyone of the three mentioned below:

1. From Ashadha Shukla Dwadashi till Kartik Shukla Dwadashi.
2. From Ashadha Purnima till Kartik Purnima.
3. Karkat Sankranti (marks the transition of the Sun into Karka-rashi. This also marks the end of the six-month Uttarayana period of Hindu calendar, and the beginning of Dakshinayana, which itself end at Makar Sankranti) that is starting from Saura-shravan till Saura-kartik

The details of the timings for Chaturmasya-vrata are also mentioned in Hari Bhakti Vilas.

ekādaśyāntu gṛhnīyāt samkrātau karkaṭasya tu
āsāḍhyām vā naro bhaktyā cāturmāsyoditam vratam

One should observe the Chaturmasya-vrata with devotion starting from sayan-ekadashi or karkat Sankranti or Ashadha Purnima.

The importance of observing Chaturmasya-vrata is mentioned in Bhavishya Purana as follows:

yo vinā niyamam martyo vratam vā japyameva vā
cāturmāsya nayenmūrkho jīvarapi mṛto hi saḥ

“One who spends the time of Chaturmasya without following the prescribed rules and regulations, without observing any vow and without chanting the names of the Lord should be considered as dead, though he is alive.”

In shastras, strict rules and regulations have been mentioned for the observance of Chaturmasya-vrata, but the minimum requirement for a sadhaka is that they should avoid eating pointed gourd, all types of beans, eggplant, bottle gourd, water spinach (kalami-shaka), malabar spinach & black lentil for all the four months.

rucyam tutkāla labhyam phalamūlādi varjayet

The seasonal fruits and vegetables allures the tongue and makes one forget Lord Hari. Overly consumption of those fruits and vegetables makes one strongly attached to the non-eternal things of this world. Therefore all those eatables which are palatable to the tongue are to be avoided during these four months and one should constantly engage himself in Hari-kirtan.

Besides this, one should not eat any kind of leafy vegetables in Shravan month, curd in Bhadra month, milk in Aswin month and non-veg (amisa) in Kartik month.

śrāvaṇe varjayecchākam dadhi bhādrapade tathā
dugdhamāśvayuje māsi kārtike cāmiṣam tyajet

As it is specifically mentioned that one should not eat non-veg in Kartik month does not mean that one can eat it in the rest of the three months. When it is mentioned that, even the vegetarian food, whatever is palatable to the tongue is to be avoided during all the four months, how come one may think that non-vegetarian food is to be allowed? More importantly as Vaishnavas’ never eat anything except Vishnu-prasad, then the question of eating non-veg is meaningless. Exact meaning of amisa in this context is palatable delicious food and not the non-veg in specific.

In the month of Kartik, it is prohibited to consume or apply oil on the body. Just to manage their living, in Kartik-vrata some people take vow to leave the four activities of eating i.e chewing, sucking, drinking and swallowing. They just eat boiled rice (Atap rice: easy-cook rice) and some eat those foods which are cooked in clarified butter. Those who observe Chaturmasya-vrata do the worshiping of Lord Hari every day after taking bath, and also, if possible, they eat once in a day.

In these four months when Lord Hari enacts the pastimes of sleeping, it is prohibited for us to sleep on soft and comfortable mattress, instead one should sleep on the floor. It is also prohibited to groom (i.e. shaving, cutting hair and nails) oneself with the motive to look good.

Those who are incapable of following the do's and don’ts of Chaturmasya-vrata due to any bodily disease or disability should sincerely chant at least one lakh round and should hear the discourses of Lord Hari with great endeavors on an everyday basis. During the observance of the vrata, the service of Vaishnavas and Lord Hari should be given the utmost importance.