Question Summary:
I would like to ask what is the difference between halal, mustahab,mubah , wajib and sunnat. Also haram, makruhe tahrimi, makruh…etc. How to decide whether particular act is haram or makruh.

Question Detail:

I would like to ask what is the difference between halal, mustahab,mubah , wajib and sunnat. Also haram, makruhe tahrimi, makruh...etc. How to decide whether particular act is haram or makruh.

Also, regarding cutting of hairs on chest,legs and thighs for both men and women, you had replied that it is permissible but undesirable. What does that  mean? If i do perform that act will i be sinful?
If possible, please provide reference from authentic books.

Answer :

In the name of Allah, Most Gracious, Most Merciful
Assalaamu `alaykum waRahmatullahi Wabarakatoh
The terms which you have cited are used in Shariah with specific academic definitions. There are many subtle distinctions between them which could only be recognized by one who has mastered the principles of fiqh. Many books are taught in Islamic institutions which state the definitions, differences and applications of these terms. Since they are rather abstruse, it would be recommended that a layman refer to the Ulama in order to seek a verdict on any action. Listed hereunder are simplified definitions and basic terminological differences. This list merely gives a brief illustration to how they differ and in no means covers all the differences.  
HALAAL/MUBAH- ‘‘That which is permissible in shariah and a person won't be punished on leaving it out.’’ (Mujam al mustalaha'atwal alfaazil fiqhiyyah 1/585, At ta'reefaat 66, Al Mufradaat 182)
Some Ulama make a distinction between halaal and mubah. ''Halaal is that for which no clear prohibition has been mentioned, whereas mubah is where a choice has been given.''(Mujam al mustalahaat 585)
SUNNAH-''It refers to the statements, actions and approval of Nabi (sallallahu alayhi wasallam).''(Tasheel usoolus shashi 145) ''It also refers to the actions and statements of Sahabah.''(Nurul anwaar 171, 179)''A person will be encouraged to carry it out without it being imposed on him.''(ibid 170) ''A person who leaves out a sunnatul huda (those practices which Nabi (sallallahu alayhi wasallam) carried out with the intention of worship, and not just as a human practice) will be sinning and therefore he will be entitled to rebuke'' (ibid 171)   
MUSTAHAB-''It is that action which Nabi (sallallahu alayhi wasallam) or Sahabah practiced upon seldomly.''(Bahishti zewar 11/4)''By practicing upon it a person will be rewarded but by leaving it out he wont get any sin.''(ibid, Raddul muhtaar 1/123)''Fuqaha also term it as nafil, mandub and tatawu.''(ibid)Hence you can see there is no difference between these terms.
The difference between sunnah and mustahab is ''whatever Nabi (sallallahu alayhi wasallam) was persistent upon with leaving it out casually without an excuse is sunnah, and whatever was done without persistence, or Nabi (sallallahu alayhi wasallam) never even do it, but merely encouraged towards it will be termed mustahab.''(Raddul muhtaar 1/123)
WAJIB-''It is that which is established from a dhanni daleel (inexplicit and unconcrete proof) , whoever leaves it out without a valid excuse will be termed a faasiq and will be deserving of punishment. Whoever rejects it will also be a faasiq and not a kaafir.'' (Bahihti zewar 11/4)''If a 'strong' command is established with a dhanni proof, this is called wajib.''(At taqreer wat tahbeer 2/107)''Wajib is established from a doubtful proof or denotion.''(Raddul muhtaar 1/639)
 “It is that which is established from such a proof which has the element of doubt.” (Tasheel usoolus shaashi 197, Nurul anwaar 170) A person who denies it will not be a kaafir''(ibid 170)
HARAAM- The opposite of halaal is haraam. ''It refers to that action which is divinely prohibited.'' (Al Qamoosul fiqhi 85) ''Upon carrying it out, a person will be entitled to the punishment of the (fire of hell).'' (Durrul mukhtaar 6/337)'' It is that which is established through a daleel qatie (explicit and concrete). Whoever denies it will be a kafir. If a person perpetrates it without a valid excuse will be a faasiq and entitled to sin.''(Bahishti zewar 11/4 Kutub khana isha'at islaam)''It is that which is established which is established with a 'strong' proof and has a 'strong' denotion''.(Raddul muhtaar 6/337)
MAKROOH TAHREEMY-''It is that which is established with a daleel dhanni . A person who refuses it will be a faasiq, and who practices upon it will be a sinner.''(Bahishti zewar 11/4) ''If there is a clear cut  prohibition, but the proof is dhanni, it is makrooh tahreemy''(Raddul muhtaar 1/132)''It is closer to haraam.''(ibid 1/131,)''When makrooh is mentioned alone it refers to makrooh tahreem'' (ibid, 1/224, 6/337)''It is that which is prohibited with a doubtful proof.''(Mustalahaatul madhaahibil fiqhiyyah 47)        
MAKROOH TANZEEHI- ''A person won't be punished for doing it, but he'll be rewarded for leaving it out.''(Raddul muhtaar 6/337, Bahishti zewar 11/4, At tauqeef 673) ''It is better to leave it out'' (At ta'reefaat) ''It is that which is better to leave out than do, and this is also the meaning of khilaaf aula ….. If the proof is not a clear prohibition but only a mere suggestion it's makrooh tanzeehi.''(Raddul muhtaar 1/132)
''The person doing it knows that to leave it out is better, although by doing it there is no sin. (Al mahsool 1/104)
''The difference between haraam and makrooh tahreemy is that haraam is established from daleel qatie while makrooh tahreemy is established with daleel  dhanny''(Mustalhaatul madhaahibil fiqhiyyah 47)
This would answer the second part of your question, that in order to understand whether a particular act is haraam or makrooh you would have to look at the daleel (proof).If it is established from a 'strong' proof it would be haraam (you would have to refer to the principles of hadith and fiqh to see whether its strong or doubtful) and if it is established from a 'doubtful' proof it would be makrooh. (Jam'ul jawaami bi sharhil mahilly 1/80, Al mujeez 21, Al mausooatul fiqhiyyah 10/206)A person would need sufficient knowledge in Quraan, hadith and fiqh including their sciences to be able to decide whether a particular act is haram or makruh.
''In order to know the difference between makrooh tahreemy and makrooh tanzeehi you have to look at the proof. If it is an emphatic command with a dhanni proof, it would be tahreemy. And if it is just a mere suggestion, without an emphatic proof it is tanzeehy.''(Raddul muhtaar 1/639)''Makrooh tahreemy is closer to haraam whereas makrooh tanzeehy is closer to halaal.''(Durrul mukhtaar 6/337)
It is clear from the above that these definitions have many academic backgrounds to them and such discussions will be truly appreciated only by academics.
B) It is permissible in the sense that it won’t constitute a sin. (Raddul muhtaar 6/407, Bahishti zewar 830, Fataawaa Mahmoodiyyah 19,444)
And Allah knows best
Wassalam
Ml. Ismail Moosa,
Student Darul Iftaa
Checked and Approved by:
Mufti Ebrahim Desai
Darul Iftaa, Madrassah In'aamiyyah