Salary on due basis or paid

Yes he can claim relief u/s 89 for arrears of salary

Relief under section 89 is available in respect of returns of earlier years filed. Otherwise not.

Here you should ask for salary certificate for 4-5 months salary. Employer must have made provision of salary payment in books of accounts.

Just booked Income from salary on current year and Claim TDS thereon

Thanks for ur reply but I don't understand it what u want to say please elaborate it more.

I want to say that club last year salary income in current year ITR. Claim TDS in current year ITR

Madam I mentioned in my question that he received whole 4-5 month salary of 2019-20 in F y 2020-21 so salary is already increased by that amount there is no question of clubbing and how we claim TDS on that because tax has been deducted in consistent with salary there is no excess tax deduction on it. Please.

Okk.. Understood...

Ask your company for Form 16A, you will get exact details of salary.

Also no need to club salary of last year if no TDS deducted.

Also salary is taxable in Income tax on due or receipt whichever is earlier basis. So, as your salary due in last year , no need to club it in current year

Madam as you rightly said that it is taxable on due or receipt basis and no need to club it if no TDS but as I mentioned TDS was deducted in FY 2020-21 when salary actually paid so in that situation wheather we file ITR of fy 2019-20 showing 4-5 month salary which was due in that FY and don't show that salary in FY 2020-21or we should take whole salary in fy 2020-21 and claim relief under sec 89 when we will file ITR of Fy 2020-21.

Firstly ask the Complany for Form 16A, then only decide whether to show it as arrear or not. How company deal with it will be shown in Form 16

Salary is always TAXABLE on due or receipt basis. which ever is earlier.
you can claim 89 relief for salary arrears

Actually it is your company's mistake. They have to file revised TDS returns for FY 20-21 and FY 19-20 and show salary and TDS for FY 19-20. But its pointless for you since due date for filing IT returns for FY 19-20 is already over. 

Sensible thing to do would be to simply consider it as income from salary of FY 20-21 and claim TDS for FY 20-21. Due date yet to be notified..Also arrears benefit is available only when income has suffered higher tax than what it was supposed to..pls check it out.