Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 195
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 195, with English translation by Maimonides (Rambam).
ליתן צדקה, שנאמר: "פתוח תפתח את ידך" (דברים טו,ח; דברים טו,יא).
To give charity, as [Deuteronomy 15:8] states: "You shall surely open your hand [to your poor brother]."