Abu Hurayra reported that the Prophet, may Allah bless him and grant him peace, said, “The person who strives on behalf of the widows and poor is like those who strive in the way of Allah and like those who fast in the day and pray at night.”
حَدَّثَنَا إِسْمَاعِيلُ قَالَ‏:‏ حَدَّثَنِي مَالِكٌ، عَنْ ثَوْرِ بْنِ زَيْدٍ، عَنْ أَبِي الْغَيْثِ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم‏:‏ السَّاعِي عَلَى الأَرْمَلَةِ وَالْمَسَاكِينِ كَالْمُجَاهِدِ فِي سَبِيلِ اللهِ، وَكَالَّذِي يَصُومُ النَّهَارَ وَيَقُومُ اللَّيْلَ‏.‏
Reference : Al-Adab Al-Mufrad 131
In-book reference : Book 7, Hadith 3
English translation : Book 7, Hadith 131