وَسَبِّحْ بِحَمْدِ رَ‌بِّكَ قَبْلَ طُلُوعِ الشَّمْسِ وَقَبْلَ الْغُرُ‌وبِ (and proclaim His purity along with your Lord's praise before sunrise and before sunset... 50:39). The imperative verb sabbih is derived from the infinitive tasbih which originally means to declare or proclaim the purity of Allah. This comprehends the verbal declaration or proclamation and the worship, such as prayer. Therefore, some scholars say that tasbih before sunrise refers to the morning prayer, and tasbih before sunset refers to ` Asr (late afternoon) prayer. Sayyidna Jarir Ibn ` Abdullah ؓ reports from the Holy Prophet ﷺ [ as part of a long Tradition ]

اِن اسَطَعتُم اَن لَّا تُغلَبُوا عَلیٰ صَلَوٰۃِ قَبلَ طُلُوعِ الشَّمسِ وَقَبلَ غُرُوبِھَا، یَعنِی اَلعَصرَ وَ الفَجرَ ثُمَّ قَرَأ جَرِیر ؓ قَبْلَ طُلُوعِ الشَّمْسِ وَقَبْلَ الْغُرُ‌وبِ ۔ (بخاری و مسلم و اللفظ لمسلم)

"So if you can avoid missing the prayer before the sunrise and the prayer before sunset, that is the 'Asr prayer and the morning prayer, you must do so." (Bukhari and Muslim the wordings of Muslim: vide Qurtubi)

Although according to the majority of commentators, tasbih in the verse refers to salah (prayer), yet the general words of tasbih include all those invocations also the recitation of which is encouraged by authentic ahadith at the time of morning and evening. Bukhari and Muslim have recorded a Tradition on the authority of Sayyidna Abu Hurairah ؓ that the Holy Prophet ﷺ said:

"If you recite morning and evening سُبحَانَ اللہ subhanallah a hundred times, no one will bring, on the Day of Judgment, a virtuous act better than it, except those who would recite the same tasbih in the same number or even more than that."

In the same collections, a narration by the same authority, says that whosoever recites subhanallahi wa bi hamdihi one hundred times in a day, his sins will be forgiven, even though they may be more than the waves of the sea. (Mazhari)