حَضَرَ صَيَاقِلَةٌ — The ṣayāqilah arrived; nominative subject with tanwīn.
رَأَيْتُ صَيَاقِلَةً — I saw the ṣayāqilah; accusative object with tanwīn.
مَرَرْتُ بِصَيَاقِلَةٍ — I passed by the ṣayāqilah; genitive after a preposition with kasra and tanwīn.
Contrast بِصَيَاقِلَةٍ (fully declinable) with بِمَسَاجِدَ (diptote).
Opening interactive controls...
Diptote Causes — Ultimate Broken-Plural Patterns
حَضَرَ صَيَاقِلَةٌ — The ṣayāqilah arrived; nominative subject with tanwīn.
رَأَيْتُ صَيَاقِلَةً — I saw the ṣayāqilah; accusative object with tanwīn.
مَرَرْتُ بِصَيَاقِلَةٍ — I passed by the ṣayāqilah; genitive after a preposition with kasra and tanwīn.
Contrast بِصَيَاقِلَةٍ (fully declinable) with بِمَسَاجِدَ (diptote).