The Messenger of Allah (may Allah's peace and blessings be upon him) forbade wearing silk except for the width of two, three, or four fingers.
Authentic hadithعن عمر بن الخطاب رضي الله عنه أَنَّ رَسُولَ الله صلى الله عليه وسلم «نهى عن لُبُوسِ الحَرِيرِ إلا هكذا، ورَفَعَ لنا رسول الله صلى الله عليه وسلم أُصْبُعَيْهِ: السَّبَّابَةَ، والوُسْطَى». ولمسلم «نهى رسول الله صلى الله عليه وسلم عن لُبْس ِالحَرِيرِ إلا مَوْضِعَ أُصْبُعَيْنِ، أو ثلاثٍ، أو أربعٍ».
‘Umar ibn Al-Khattāb (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) forbade wearing silk except for this much, and he raised his index and middle fingers to us. A narration by Muslim reads: "The Messenger of Allah (may Allah's peace and blessings be upon him) forbade wearing silk except for the width of two, three, or four fingers.”
Explanation
The Messenger of Allah (may Allah's peace and blessings be upon him) forbade wearing silk for males, except for the amount he specified. According to the Hadīth agreed upon by Al-Bukhāri and Muslim, this amount is the width of two fingers. In the Hadīth of Muslim, it is the width of two, three, or four fingers. So, the biggest width (four fingers) is to be accepted. Thus, there is nothing wrong in wearing silk with the width of four fingers.
Source · Narrated by Bukhari & Muslim
From the Hadith Encyclopedia (hadeethenc.com).