Imam Ahmad recorded in his Musnad, that a person who was riding behind the Prophet said, “The Prophet’s animal tripped, so I said, `Cursed Shaytan.’ The Prophet said,
لَا تَقُلْ: تَعِسَ الشَّيْطَانُ، فَإِنَّكَ إِذَا قُلْتَ: تَعِسَ الشَّيْطَانُ، تَعَاظَمَ وَقَالَ: بِقُوَّتِي صَرَعْتُهُ، وَإِذَا قُلْتَ: بِاسْمِ اللهِ تَصَاغَرَ حَتى يَصِيرَ مِثْلَ الذُبَابِ
Do not say, ‘Cursed Shaytan,’ for if you say these words, Satan becomes arrogant and says, ‘With my strength I made him fall.’ When you say, ‘Bismillah,’ Satan will become as small as a fly.
Further, An-Nasa’i recorded in his book Al-Yawm wal-Laylah, and also Ibn Marduwyah in his Tafsir that Usamah bin `Umayr said, “I was riding behind the Prophet…” and he mentioned the rest of the above Hadith. The Prophet said in this narration,
لَا تَقُلْ هكَذَا فَإِنَّهُ يَتَعَاظَمُ حَتَّى يَكُونَ كَالْبَيْتِ، وَلكِنْ قُلْ: بِسْمِ اللهِ، فَإنَّهُ يَصْغَرُ حَتَّى يَكُونَ كَالذُبَابَةِ
Do not say these words, because then Satan becomes larger; as large as a house. Rather, say, ‘Bismillah,’ because Satan then becomes as small as a fly.
This is the blessing of reciting Bismillah.
Basmalah (reciting Bismillah) is recommended before starting any action or deed. For instance, Basmalah is recommended before starting a Khutbah (speech).
The Basmalah is also recommended before one enters the place where he wants to relieve himself, there is a Hadith concerning this practice. Further, Basmalah is recommended at the beginning of ablution, for Imam Ahmad and the Sunan compilers recorded that Abu Hurayrah, Sa`id bin Zayd and Abu Sa`id narrated from the Prophet ,
لَا وُضُوءَ لِمَنْ لَمْ يَذْكُرِ اسْمَ اللهِ عَلَيْهِ
There is no valid ablution for he who did not mention Allah’s Name in it.
This Hadith is Hasan (good). Also, the Basmalah is recommended before eating, for Muslim recorded in his Sahih that the Messenger of Allah said to `Umar bin Abi Salamah while he was a child under his care,
قُلْ بِسْمِ اللهِ وَكُلْ بِيَمِينِكَ وَكُلْ مِمَّا يَلِيكَ
Say Bismillah, eat with your right hand and eat from whatever is next to you.
Some of the scholars stated that Basmalah before eating is obligatory. Basmalah before having sexual intercourse is also recommended. The Two Sahihs recorded that Ibn `Abbas said that the Messenger of Allah said,
لَوْ أَنَّ أَحَدَكُمْ إِذَا أَرَادَ أَنْ يَأْتِيَ أَهْلَهُ قَالَ: بِسْمِ اللهِ اللَهُمَّ جَنِّبْنَا الشَّيْطَانَ وَجَنِّبِ الشَّيْطَانَ مَا رَزَقْتَنَا،فَإنَّهُ إِنْ يُقَدَّرْ بَيْنَهُمَا وَلَدٌ لَمْ يَضُرَّهُ الشَّيْطَانُ أَبَدًا
If anyone of you before having sexual relations with his wife says, ‘In the Name of Allah. O Allah! Protect us from Satan and also protect what you grant us (meaning the coming offspring) from Satan,’ and if it is destined that they should have a child then, Satan will never be able to harm that child.