Sayyiduna Abdullah bin Mas'ud (may Allah be pleased with him) said: "If I were to become ritually impure (junub) and then not find water for a month, even then I would not pray."
Sufyan (al-Thawri) said: This is not acted upon.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 9217