It is narrated from Sayyiduna Salman al-Farisi (may Allah be pleased with him): "Prayer is a measure. Whoever fulfils it completely will be given his reward in full, and whoever falls short, you know well what has been said about those who give short measure."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 3586