Is there any formal statement in this regard by Newton? Want to know what exactly Newton stated in this regard.
It is not generally recommended to try to learn Newtonian mechanics directly from the writings of Newton. Newton had the first word on his theory, but not the last word. Many issues that were unclear or confusing in Newton's day have been clarified by subsequent researchers. So it is generally preferable to learn from modern didactical sources.
However, Newton's Principia did have several relevant quotes:
First, Newton believed in absolute space and time, so his conception of the principle of relativity was more of a practical equivalence. In the definitions he said
Absolute, true, and mathematical time, of itself, and from its own nature flows equably without regard to anything external, and by another name is called duration : relative, apparent, and common time, is some sensible and external (whether accurate or unequable) measure of duration by the means of motion, which is commonly used instead of true time ; such as an hour, a day, a month, a year.
Absolute space, in its own nature, without regard to anything external, remains always similar and immovable. Relative space is some movable dimension or measure of the absolute spaces ; which our senses determine by its position to bodies ; and which is vulgarly taken for immovable space
But then in the corollaries to his laws he states:
COROLLARY V. The motions of bodies included in a given space are the same among themselves, whether that space is at rest, or moves uniformly forwards in a right line without any circular motion
So he did recognize the principle of relativity as described by his predecessor, Galileo. Although Newton believed in the existence of absolute space and time, he recognized that it was not relevant to his laws. However, again, the understanding of this principle was refined considerably in the centuries since Newton, so a modern textbook would be a better source than the Principia.