"And whatever thing you spend," meaning: in obedience to Allah, "He will replace it." Al-Suddi's interpretation of "He will replace it" is: meaning in the Hereafter; that is, He will compensate them with Paradise for it.
Surah Saba, verses 40 through 42.
﴿وَمَا أَنفَقْتُم مِّن شَيْءٍ﴾ أَي: فِي طَاعَة اللَّه ﴿فَهُوَ يخلفه﴾ تَفْسِير السّديّ: ﴿فَهُوَ يخلفه﴾؛ يَعْنِي: فِي الْآخِرَة؛ أَي: يعوضهم بِهِ الْجنَّة.
سُورَة سبأ الْآيَات من الْآيَة ٤٠ حَتَّى الْآيَة ٤٢.