Built into a column near the entrance of Masjid Jamek's main prayer hall is the building's foundation stone, an engraved white marble piece placed by the Sultan of Selangor, Sultan Alaeddin Suleiman on 23 March 1908. Details about the ceremony is available at this link. Thanks to Amir Ashraf from Akademi Jawi Malaysia, we now have a complete transliteration of the inscription.
كڤد 19 صفر 1326 سنة
المسيحي 23 مارچ 1908
تله دمولاءي كاكي تيڠ مسجد اين
دڠن تاڠن يڠمها ملي السلطان علاء الدين
سليمان شاه سي ام جي
سلاڠور دار الإحسان
ماس يڠمليا ايچ سي بيلفيل
بريتيش رسيدين
دان توان ايه بي هابك
انجينير
الله جوا يڠ مڽمڤرناكن
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Kepada 19 Safar 1326 Sanah
al-Masihi 23 March 1908
Telah dimulai kaki tiang masjid ini
dengan tangan Yang Maha Mulia al-Sultan ‘Alā’ al-Dīn
Sulaymān Shāh, C.M.G
Selangor Dār al-Iḥsān
Masa Yang Mulia H.C Belfield
British Residen
Dan Tuan A.B Hubback
Engineer
Allah jua yang Menyempurnakan
Transliteration completed with assistance from Amir Ashraf, Akademi Jawi Malaysia.
(Note one error - AB Hubback was the Architect, not the Engineer)
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A translation was also published in the Malay Mail on 24 March 1908:
'The foundation stone of this Mosque was laid upon the fourteenth day of Safar by the hand of the ruler of the State, Sultan Suleiman bin Almarhum, C.M.G, Dar-ul-Ehsan, at the time when Mr. H.C Belfield was British Resident, Mr. A.B Hubback being the architect. ‘God fulfilleth all’.
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On the other side of the entrance is a new tablet commemorating the renaming of the mosque to Masjid Jamek Sultan Abdul Samad, after the 4th Ruler of Selangor who reigned from 1857 to 1898. The ceremony was officiated by the present Sultan of Selangor, Sultan Sharafuddin Idris Shah Alhaj on 23 June 2017.