Property i bought through by a registered agreement to sell

Sir, I bought a shop in a DDA market from my husband in the year 2011. The payment was made in cash as was allowed in 2011 to purchase property in cash. Since the property is a DDA property the sale was not made by a sale deed but by registering the agreement to sale and the stamp duty was paid on it, as the is the generally accepted practice. All the documents were registered with the registrar in my name. Now in the year 2018, since we are undergoing divorce proceedings, my husband has challenged the ownership on the basis that the sale deed was not executed. My question is was the sale not valid when the agreement to sell was registered and stamp duty was paid thereon? Also, is his contention not valid as per the limitation act, since he is challenging the sale made in the year 2011 in the year 2018.