What is Chillah teen chilla seroza 3 days,40 days 4 months

The Reality of Chillah
 People engaged in Tabligh stress the importance for going for a chillah.What is the reality of chillah on basis of which these people make such recommendations?

(Note :First of all in tableegh 3 days,40 days(chilla) 4 month is  system and tarteeb and it is not obligatory or fixed time period. One may go for less and more number of days depending on prevailing situation.)
But while making system for days it has been tried that time period should have some relation with Prophetic Traditions. Some of the related Ahadith are Here although tabligh is not claiming that these 40 days etc are sunnah. It is simply a system for oraganisational purpose) 

Some of the related Ahadith are here

A Hadith of Sahih Bukhari mentions that the fertilized embryo stays in the womb for forty days,after which it becomes a clot of blood.

It thereafter transforms into a piece of flesh after forty days.
After a further forty days, the sustenance, life span and other factors pertaining to the child are recorded.
This narration makes it evident that the 40 days (Chillah) plays a great role in human transformation.

2. The Ahadith also mention that performing salaah with Jamaat for forty days frees a person from hypocrisy and from Jahannam. Similarly glad tidings of receiving knowledge is given for one who makes a'aamaal consistently for forty days.

Spending a chillah (40 continuous days) doing a good deed is indeed a very blessed act which strongly affects ones soul and inner state.

3. Sayyidina Musa was given the Torah after he had secluded himself for forty days on Mount Tur.

 4. In one Hadith, the Prophet peace be upon him said;
' ' Whoever offers for forty days prayer with congregation, without missing the first Takbir shall be redeemed from the fire as well as from hypocrisy, provided he did so for the sake of Allah.
( Tirmidhi 1/33, Mishkaat p 102)

From this we learnt that chillah affects a persons state in a certain manner.

see, when a mans seed finds its way into a womans womb and settles there, the during the first forty days the 'Alaqah' turns into 'Mudhgha' (i.e the lump of flesh). Then after another forty days some parts of this 'mudhghah' is developed into bones, and then these bones are covered with flesh. then (after these three stages in forty days) life and spirit are blown into this lump of flesh and bones
(Bayanul Quran)

Once during the Caliphate of Sayyiduna Umar, a man became madly infatuated with a woman. That woman, happened to be a very modest, chaste woman. Since she was also a very prudent lady she requested someone to convey the following message to the man: Your matter will be decided only after you have offered for forty days the salah behind sayyiduna Umar, without even missing the first takbir. The person did so and after forty days, he found his state to be changed for the better. His love had turned to true love, not for the woman, but for Allah! When sayyiduna Umar was informed of this he said; ' Allah and his Messenger spoke the truth, prayer stops one from indecencies and evil. '
( Fatawa-e-rahimiyyah, 6/384)

5. In a Hadith it is reported that the Prophet of Allah said; ' If anyone worships Allah for forty days with sincerity, then Allah causes springs of wisdom to gush from his heart.'
(Ma'ariful Quran, Ruh UL Bayan)

(Adapted from mufti mahmud Hasan Gangohi & the Tablighi jamaat by Shaikhul Hadith Maulana Fadlur Rahman Azmi, and Scattered pearls, by Maulana Muhammad Yunus Palanpuri.)

As for 4 month

Umar Raziallah anhu in his Khilafat has [prescribed the maximum limit to go in path of Allah as 4 month based on an incidence in which he sought opinion from his daughter Ummul momineen Hazrat Hafsa R.A. and finally decided this.

So in Tabligh also maximum period for khuruj is 4 month for a married man.