صَلَاتِ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – صَلَاتِ is a noun

A noun may either be 1) Definite or indefinite 2) Masculine or feminine 3) Singular, dual or plural 4) Nominative, accusative or genitive

الصَّلَاةُ is the natural state of the definite noun and it becomes الصَّلَاةِ due to: 1) a preposition that precedes it or 2) a possessed noun that precedes it

الصَّلَاةِ loses it’s definite article, becoming صَلَاتِ due to it being a possessed noun

Grammatical analysis of صَلَاتِ
اسْمٌ مَجْرُوْرٌ بِالكَسْرَةِ الزَّاهِرَةِ وَهُوَ مُضَافٌ
Surah/Below are the 6 verses in the holy Quran containing the possessed nounصَلَاتِ
Verse
6-92
6-162
23-2
70-23
70-34
107-5those who, they are heedless about their prayersالَّذِيْنَ هُمْ عَنْ صَلَاتِهِمْ سَاهُوْنَ