Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.
As to what follows:
With regards to answering your question I say:
Firstly: I do not know of anyone amongst the scholars who says that a small amount of interest is allowed. There is consensus on the prohibition of interest, small or plenty. There is no difference among the scholars in this regard. This consensus was stated by the majority of scholars: Ibn ‘Abdul Barr, Ibn al-Mundhir, al-Nawawi and the rest who worked on narrations on issues which were agreed upon unanimously said that interest is not permissible, whether it is less or much. This means that if I give you Shaykh Muhammad ten Riyals, and I say to you: "Give me back ten and half Riyals after one week," then this is interest. Even if it is half Riyal, it falls under the warning given in Allah’s saying: “Those who eat Riba (usury) will not stand (on the Day of Resurrection) except like the standing of a person beaten by Shaitan (Satan) leading Him to insanity.” [al-Baqarah: 275],
and similar texts in which warnings of consuming interest were given.
However the brother has been confused by what some of our brothers say regarding the issue of shares: that they are small interest and there is nothing wrong with small interest. At this juncture, I would like to remind that this is the source of the confusion for many people who say: "How can you say small interest is permitted when Allah prohibits it, then how can small interest be permissible?"
The answer to this confusion is: the brothers who say that shares are permissible do not permit the instalment that has interest in it. What they say is: "The objective of this company is let’s say: communications, power, industry, farming, these are basically permissible services and they are the ones that motivated people to buy shares. People did not go to these entities so that they earn profitable dividends from their deposits in interest based banks, but they went to these entities because of permissible activities offered and not deposits. If they wanted to deposit and get usurious earnings they would have gone to the bank straight away. So they did this because the activity is basically permissible, and that is often the case with companies. Regarding these activities, a group of scholars said that they are prohibited regardless of if another type of an impermissible activity is prohibited in smaller quantities or not.
So they differentiated between two issues and this differentiation is so precise that it requires thorough study.
As for small amounts of alcohol which is the main issue, the Messenger of Allah (peace be on him) resolved it by saying: “What intoxicates in large amounts, a small amount of it is unlawful.” This hadith is in the authentic books of hadith and others. This clarifies to us that it is compulsory to avoid alcohol, even if someone says: I swear by Allah, I do not get drunk so I want to drink. It is well known that the probability of drunkenness establishes the ruling of the prohibition of a substance . This means that if a person has the ability of remaining sober if he drinks one or two bottles and does not get drunk, do we say to him: "Drink and there is nothing wrong with a small amount, " No, there is no doubt that the reason of the ruling is that alcohol intoxicates. Therefore, if a person does not get drunk by drinking one or two bottles or by one or two glasses of alcohol, this does not justify drinking. Therefore, smaller amounts and larger quantities of alcohol are prohibited. The Messenger of Allah (peace be on him) clarified what we mentioned in the following hadith: “What intoxicates in large amounts, a small amount of it is unlawful.” This means that what doesn’t intoxicate unless by drinking ten glasses, we do not say that three, four or five glasses of it is permissible, nay but even one dose of it is prohibited.