LessonsRules of Hāʾ al-Ḍamīr: Vowels, Ṣilah and ExceptionsQuiz

The second source example is وَيُعَلِّمُهُ الْكِتَابَ. In connected recitation, the lām of the article is sākin after the elided hamzat al-waṣl, so the hāʾ is followed by a sākin sound and receives no ordinary ṣilah.
Decide by what is actually pronounced during connection, not only by the presence of a written alif.

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No regular ṣilah before a sākin sound

Rules of Hāʾ al-Ḍamīr: Vowels, Ṣilah and Exceptions

The second source example is وَيُعَلِّمُهُ الْكِتَابَ. In connected recitation, the lām of the article is sākin after the elided hamzat al-waṣl, so the hāʾ is followed by a sākin sound and receives no ordinary ṣilah.
Decide by what is actually pronounced during connection, not only by the presence of a written alif.