In Vasudev Dhanjibhai Modi v. Rajabhai Abdul Rehman & Ors.,  l SCR 66, a decree for possession was passed by the Court of Small Causes which was confirmed in appeal as well as in revision. In execution proceedings, it was contented that the Small Causes Court had no jurisdiction to pass the decree and, hence, it was a nullity.
Rejecting the contention, this Court stated:
“a Court executing a decree cannot go behind the decree : between the parties or their representatives it must take the decree according to its tenor, and cannot entertain any objection that the decree was incorrect in law or on facts. Until it is set aside by an appropriate proceeding in appeal or revision, a decree even if it be erroneous is still binding between the parties. Suffice it to say that recently a bench of two-Judges of this Court has considered the distinction between null and void decree and illegal decree in Rafique Bibi v. Sayed Waliuddin,  l SCC 287. One of us (R.C. Lahoti, J. as his Lordship then was), quoting with approval the law laid down in Vasudev Dhanjibhai Modi, stated:
“What is ‘void’ has to be clearly understood. A decree can be said to be without jurisdiction, and hence a nullity, if the court passing the decree has usurped a jurisdiction which it did not have; a mere wrong exercise of jurisdiction does not result in a nullity. The lack of jurisdiction in the court passing the decree must be patent on its face in order to enable the executing court to take cognizance of such a nullity based on want of jurisdiction, else the normal rule that an executing court cannot go behind the decree must prevail.
Two things must be clearly borne in mind. Firstly, ‘the court will invalidate an order only if the right remedy is sought by the right person in the right proceedings and circumstances. The order may be a ‘a nullity’ and ‘void’ but these terms have not absolute sense: their meaning is relative, depending upon the court’s willingness to grant relief in any particular situation. If this principle of illegal relativity is borne in mind, the law can be made to operate justly and reasonably in cases where the doctrine of ultra vires, rigidly applied, would produce unacceptable results.’ (Administrative Law, Wade and Forsyth, 8th Edn., 2000, p. 308). Secondly, there is a distinction between mere administrative orders and the decrees of courts, especially a superior court. ‘The order of a superior court such as the High Court must always be obeyed no matter what flaws it may be thought to contain. Thus, a party who disobeys a High Court injunction in punishable for contempt of court even though it was granted in proceedings deemed to have been irrevocably abandoned owing to the expiry of a time-limit.’ (ibid., p. 312) A distinction exists between a decree passed by a court having no jurisdiction and consequently being a nullity and not executable and a decree of the court which is merely illegal or not passed in accordance with the procedure laid down by law. A decree suffering from illegality or irregularity of procedure, cannot be termed inexecutable by the executing court; the remedy of a person aggrieved by such a decree is to have it set aside in a duly constituted legal proceedings or by a superior court failing which he must obey the command of the decree. A decree passed by a court of competent jurisdiction cannot be denuded of its efficacy by any collateral attack or in incidental proceedings.”