Ya ayyuha allatheena amanoo itha najaytumu arrasoola faqaddimoo bayna yaday najwakum sadaqatan (surah Mujadilah: 12)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(58:12) Believers, when you come to the Messenger for private consultation, offer some charity before your consultation with him. *29 That is better for you and more conducive to purity. But if you find nothing to offer in charity, then know that Allah is Most Merciful, Most Compassionate.

Yaaa ayyuhal lazeena aamanooo izaa naajitumur Rasoola faqaddimoo baina yadai najwaakum sadaqah; zaalika khairul lakum wa athar; fa il lam tajidoo fa innal laaha ghafoorur Raheem

*29) according to Hadrat 'Abdullah bin 'Abbas, this Command was sent down because the Muslims had started requesting the Holy Prophet (upon whom be Allah's peace) for private counsel much too frequently; and this put him to great inconvenience. At last, Allah willed to relieve His Prophet of this burden.. (Ibn Jarir). Zaid. bin Aslam says that the Holy Prophet (upon whom be Allah's peace) would never turn down the request of anyone, who wanted to consult him in private. Whoever desired to have private counsel with him, he would oblige him Often it so happened that the people would ask for private counsel in matters in which there was no real need. This was the time when all of Arabia was engaged in war against Madinah. Sometimes after a person had made such a request, Satan would' whisper into the ears of the people the idea that he had brought to the Holy Prophet the news of invasion by such and such tribes, and this would cause numours to spread in Madinah. On the other hand, this would give the hypocrites an opportunity to say that Muhammad (upon whom be Allah's peace) was a credulous person, who listened to and believed in whatever anyone told him. Because of this AIlah imposed the restriction that anyone who wanted to have private counsel with the Prophet should first give away something in charity. (Ibn 'Arabi: Ahkam al-Qur an). Qatadah says that some people talked to the Holy Prophet in private in order to show their superiority to others.
Hadrat 'Ali says when this was enjoined the Holy Prophet asked him, What should be the quantity of the charity? Should it be one dinar? I said: This is more than the people can afford. The Holy Prophet then asked: Should it be half a dinar? I said: This too is too much. Then he asked what it should be. I said . Gold equal to a barley grain. The Holy Prophet remarked: Your advice is for too little! " (Ibn Jarir, Tirmidhi, Musnad Abu ya'/a). In another tradition Hadrat `Ali says: "This is a verse of the Qur'an which no one acted upon except me. As soon as it was enjoined, I offered the charity and consulted the Holy Prophet about a problem. " (Ibn Jarir, Hakim, lbn al-Mundhi, `Abd bin Humaid).