Sahih al-Bukhari, Book 56, Hadith 202 (In-Book)

Narrated Jabir bin `Abdullah: Whenever we went up a place we would say, "Allahu--Akbar (i.e. Allah is Greater)", and whenever we went down a place we would say, "Subhan Allah."

حَدَّثَنَا مُحَمَّدُ بْنُ يُوسُفَ، حَدَّثَنَا سُفْيَانُ، عَنْ حُصَيْنِ بْنِ عَبْدِ الرَّحْمَنِ، عَنْ سَالِمِ بْنِ أَبِي الْجَعْدِ، عَنْ جَابِرِ بْنِ عَبْدِ اللَّهِ ـ رضى الله عنهما ـ قَالَ كُنَّا إِذَا صَعِدْنَا كَبَّرْنَا، وَإِذَا نَزَلْنَا سَبَّحْنَا‏.‏

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