Kitaab At-Tawheed, Chapter: 53 Whoever Asks in the Name of Allah Should Not Be Refused
It is reported on the authority of Ibn `Umar (ra) that he said: "Allah's Messenger 
said:
"Whoever asks for something in Allah's Name, give it to him; if anyone seeks refuge in Allah's Name, give him refuge; if anyone gives you an invitation, accept it; and if anyone does you a kindness, recompense him; but if you have not the wherewithal to do so, pray for him until you feel that you have recompensed him."
(Narrated by Abu Dawood and An-Nasaa`i, who graded it as authentic)
The Prophet commands us in this Hadith to help whoever asks for assistance in Allah's Name in all that does not entail disobedience to Allah and His Messenger ; and to protect from evil whoever seeks protection in Allah's Name; and to accept an invitation when one is invited, so long as it does not entail anything forbidden;1 and to respond in kind to those who do favours for us; He also said that, if we are unable to respond in kind, then we should supplicate Allah on their behalf until we feel that we have repaid them in full. If we do all of these things, the result will be to foster brotherly love, compassion, generosity and unity amongst the Muslim community and put an end to enmity, division, strife, miserliness and disunity.
Benefits Derived From This Hadith
1. The obligation to give to the one who asks in Allah's Name.
2. The obligation to defend from evil the one who seeks shelter in Allah's Name.
3. The obligation to accept a brother Muslim's invitation to a meal, a wedding celebration, birth celebration etc. so long as doing so does not involve anything forbidden.
4. The obligation to recompense those who do good to us.
Relevance of This Hadith to the Subject of the Chapter
That it proves the obligation to give to whomsoever what is asked in Allah's Name.
Relevance of This Hadith to the Subject of Tawheed
That it proves that it is forbidden to refuse a person in need when he asks in Allah's Name because to do so is to fail to glorify Allah , as is His right upon us, and this conflicts with correct Tawheed.
Footnotes
1. For example, were one to be invited to a gathering where, drinking of alcoholic beverages, playing of music, smoking, playing of games of chance etc. were taking place, it would not be obligatory to attend; rather, it would be obligatory to decline the invitation.