No. Some extremists who prefer literal interpretation of the Qur'an and Ahadith and who make up their own rules have invented that rule, too. Here is an explanation on the Islamic position of using numbers from a reliable source.
Numeral 786 as Basmala
http://qa.sunnipath.com/issue_view.asp?HD=1&ID=688&CATE=115
To write 786 in lieu of the Basmala is permitted. The numeral 786 represents the abjad [letter-numeral] value of the Basmala [‘Bismillaah al-Rahmaan al-Raheem’]. If there is fear of disrespect for the Basmala if written in full then it may be preferable to use the number 786 instead. Occasional use of abjad numerals has long been current among the Ulema.
...
Objections to using 786 in the sense of the Basmala fall into three categories:
1. The objection that the numeral 786 does not represent the Basmala. This is simple ignorance of abjad values. Such an objection carries no weight at all.
2. The objection that using 786 is a novelty. This is correct but so is the spread of printed matter and worldwide literacy. The Sunna way in this regard is to find ways to curb the risks of heedlessness and disrespect to sacred things in print. The use of 786 is one such way. A better one is to write the Arabic letter Ba' to stand for the Basmala or to write: Bismihi Ta`ala = "In his Name, Most High."
An important point of principles. The use of abjad numerals was accepted by the Ulema of Islam East and West long ago and therefore cannot be called a bid`a except by those constantly and/or essentially at odds with the Umma's understanding and practice i.e. the bid`a sects themselves. They can be exposed by their own key statements, such as "Was the verse, 'Today I completed your religion for you', revealed to the Prophet (pbuh) or to the so-called scholars of our age who are all bent to amend the Divine principles?"
3. The objection that it is potential kufr because 786 also happens to stand for the abjad value of "Hare Krishna" if Arabized as Ha'-Ra'-Ya'-Kaf-Ra'-Shin-Nun-Alif. This is a grave charge and false on many fronts or rather backsides to boot. It is ironic that this objection was published in a country that has allowed the name of their king to be engraved on the very door of the Ka`ba in full letters, yet they do not raise a peep against such an act! More importantly:
(i) False witness against fellow Muslims, chronic suspicion of fellow Muslims, and diseased pride are all among the Kaba'ir. They must be avoided at all cost and such an accusation should have never seen the light of day nor be given the time of day. Instead, it is being reposted and circulated!
(ii) Those that leveled these false accusations of potential kufr and bid`a against Muslims should repent, as the accusations have now returned upon them. The same applies to the propagators. Allah Most High has placed the Hurma or sanctity of a Muslim too high to allow such reckless accusations to be thrown about without consequences.
(iii) The correct abjad value of Hare Krishna is NOT 786 but 776. There is no long Ya at the end of Hare but a brief vowel that does not stand for a letter. The result is: NOT h-5, r-200, i-10, k-20, r-200, sh-300, n-50, a-1 = Aggregate 786 BUT h-5, r-200, k-20, r-200, sh-300, n-50, a-1 = Aggregate 776
(iv) The numeral 786 might apply to any number of names or phrases. However, it is used by Muslims only and in the Basmala sense only. Other senses are precluded from the usage of those Muslims. A pseudo-censor comes along and claims that other senses are not precluded: such a false judge is ignoring the fundamental principles that {Deeds Count Only According to Intentions} and that {The Lawful Is Crystal Clear and the Unlawful is Crystal Clear}.
He has put aside half of the Shari`a by ignoring these two principles. Who will possibly follow him except those Allah misguides? The reverse is true also: even if 786 meant only ‘Bismillaah al-Rahmaan al-Raheem’ and nothing else, it would still be meaningless to use it without the intention of Basmala.
(v) Suppose 786 does stand for Hare Krishna, which means "Holy Krishna." There is nothing in Islam - and Allah knows best - that precludes the possibility that Krishna was a Prophet of Islam. "We find popular Muslim poets in India, such as Sayid Sultan, writing poems about Krishna as a Prophet. There is no final theological proof that he was one, but the assumption is nonetheless not in violation of the Koran" (Abd al-Hakim Murad, "British and Muslim?" Based on a lecture given to a conference of British converts on September 17 1997). Writing the name of a Prophet as one's letterhead can never be "infidelity."
Someone had requested a response on this issue two years ago on the mail-list msa-ec. The lengthiness of this response is due to the sad fact that extremism has shifted the issue from a one-line ruling of secondary importance (Use of the numeral 786 in lieu of Basmala offensive or permitted? - Permitted) to the grave disease of takfir and tabdi`, and Allah is our help.
{And speak not, concerning that which your own tongues qualify (as clean or unclean), the falsehood: "This is lawful, and this is forbidden," so that ye invent a lie against Allah. Lo! those who invent a lie against Allah will not succeed} (16:116).
Hajj Gibril Hadad