The source gives practical limits:
• By day, more than 4 voluntary rak'ahs under one Salaam is disliked.
• By night, more than 8 under one Salaam is disliked.
• Abu Hanifah preferred four-rak'ah sets by day and night.
• Abu Yusuf and Muhammad preferred 2-by-2 at night, and the text says this is followed for fatwa.
The source also says night prayer is better than daytime voluntary prayer, and longer standing is preferred to merely multiplying prostrations.
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Emphasized Sunnahs and Other Voluntary Prayers
The source gives practical limits:
• By day, more than 4 voluntary rak'ahs under one Salaam is disliked.
• By night, more than 8 under one Salaam is disliked.
• Abu Hanifah preferred four-rak'ah sets by day and night.
• Abu Yusuf and Muhammad preferred 2-by-2 at night, and the text says this is followed for fatwa.
The source also says night prayer is better than daytime voluntary prayer, and longer standing is preferred to merely multiplying prostrations.